Whether you’re running MATE, Cinnamon, XFCE, KDE or something else that keeps things classic, there’s clearly something about the traditional desktop layout that keeps pulling people in.
I can’t be just because of resource usage? The familiarity? The customization?
Did you try a more modern DE and come back, or have you always preferred classic DEs?
No wrong answers here, genuinely interested in what keeps people on the traditional side of things.
For me it’s the Mate desktop. I’ve never used anything but Ubuntu since 2007 and with 10.04 it became my daily driver and I used it until it reached EOL. Then Unity became the default desktop but thankfully Ubuntu MATE came along shortly thereafter and eventually became an official flavor and I’ve never used anything but LTS releases since. I’ve fiddled with other Debian based distros but always came back to UM.I like the simplicity and familiarity of the Mate desktop and will continue to use it as long as it exists.
That caught me out as well. I really tried for like a few months to stick with Unity. But it was so bad. Sometimes I wonder if Unity was never released by Ubuntu and that experience never happened, maybe we would have been more tolerant of snap packages. 
Apparently there were enough folks that liked it that Ubuntu Unity became an official flavor. But I just could never used to it back in the day.Not a big Snap guy either,I keep the core Snaps as I’m a little afraid of breaking something by removing them otherwise everything else is .deb based on my machine.
Most of the time I don’t want to think about my desktop, I need to get stuff done & thus want the DE/WM to just stay out the way so I can work etc.
The first ‘home’ that I really appreciated I think was GNOME 2, alas that was really when it was disappearing & GNOME Shell (3) was being introduced. From there I moved to KDE Plasma; lost interest with Plasma 5 & went to Xfce… I was asked to join the Lubuntu team so started using LXQt (it was replacing LXDE for them at the time), so I’ve moved around a lot over the years.
I’m always happy when using Xfce, I’ve setup my LXQt so it acts pretty much like my Xfce setup anyway so I’m happy there too (outside of media keys which I could change; but haven’t to keep my config mostly standard), and MATE somewhat allows me to pretend I’m back using GNOME 2 of long ago (its not, but I’ve also moved on a little since then anyway; my config there somewhat matches my Xfce session anyway now).
I may login to GNOME 50 if I want a different experience for a day (a change is nice now and again), but I really can only cope with that occasionally as after a few hours find it annoys me, where the traditional desktop I just don’t notice & I get stuff done.
(there are days when I can really appreciated GNOME Shell & have found it extremely time efficient, but it tends to ‘irk’ me more often than I have good days)
FYI: My installs are commonly multi-desktop installs, as such I’m selecting which I’ll use when I login and aren’t stuck to a single choice. I’ve got other installed choices than I’ve mentioned here too.
That’s exactly how I do feel!
In essence, ‘traditional’/‘classic’ desktop is efficient and familiar user interface. Some extra bells and whistles do not make it ‘modern’.
I can not deny a possibility to invent more efficient and convenient user interface. Nevertheless, I have not seen anything like that yet.
Frankly, I do not understand what ‘modern’ desktop is except for being a buzzword. To me, the more user interface deviates from classic, the more it cripples users’ experience.
I used and liked gnome2. Mate as a continuation of gnome2 is the most like it. I hate docks. I want my panel on the bottom, I want icons on the desktop and applets that make sense. I can also add often used apps to the panel for when I have windows open. That gives me three ways to access my apps. Menu, Desktop Icons and applets. I can’t think of a better setup.
I really liked the “Applications, Places, System” concept of GNOME 2 (Ubuntu 11.04). I didn’t mind Unity for its quick search feature, but when Ubuntu MATE brought it back which I stuck with it until the end of 16.04 LTS.
When GTK 3 became more a thing, I felt it ruined the GTK 2-ness of MATE. As a UI person I’m quite sensitive to that, and with the way GTK was heading, I decided to switch to a Qt-based desktop. I’m pretty happy with KDE under a dual panel arrangement. I still prefer the desktop metaphors of menu bars, toolbars, docks and status bars. That to me, is a desktop.
I actually look after some patches for GTK 3 to bring back some of that GTK 2 classic-ness, so for me KDE + GTK + Qt apps feel quite cohesive together. I repel concepts like CSD decorations.
For me, I like visibility of “everything”.
So, having a “taskbar”, the way MATE offers on the bottom panel (for my setup) is ideal … and I consider that an “advanced” design concept. After all, isn’t that what various HUDs attempt, global visibility?
The “merry-go-round” of the Cairo dock just isn’t for me!
The other “advanced” aspect is having all my “preferred service providers” (a.k.a. Apps and Notifiers) pinned to the upper panel (again, for my configuration).
When it comes down to desktops, I have pretty high demands.
I actually don’t care if a desktop is “modern” or “classic”.
I do care about functionality and flexibility.
I often regard Linux as the software equivalent of a box of LEGO® 
For me, a desktop:
must be highly configurable
I sometimes assemble computers to work as appliances.
I need to be able to bend the desktop to my will because it is part of the interface.
must have a decent ratio of functionality versus resource consumption
I’m not going to move to a desktop that eats way more CPU and RAM, adds horrible latency and gives me back less options, less functionality, less flexibility, less reliability, more unneeded complex moving parts and tries to pamper me to death.
.
If that is the definition of "modern’, then no thanks, it’s not for me.
The choice for MATE desktop has been very rewarding. It keeps things relatively simple under the hood, has the optimal balance between luxuary and flexibility and is relatively light on resources.
I use MATE for almost everything, including my mediacenter.
MATE also runs on almost anything, like my ASUS F3T laptop that is more than 20 years old
(AMD Turion X2 , 3GB RAM, nVidia GeForce Go 7300) and even plays youtube videos. 
But the desktops that I also hold in very high regard are:
XFCE (used it in the past)
Pretty much comparable to MATE, used to be a bit more spartan but AFAIK it has improved tremendously.
KDE-Plasma (Ubuntu Studio)
Used to be heavyweight but not anymore, and it is also extremely flexible, attractive and fast. If I ever have to ditch MATE then I’ll probably move to KDE
Moksha (Bodhi Linux)
Based on Enlightenment, incredibly light, beautiful, runs very very fast and snappy on my ancient <1GB netbook without ever hitting swap. It really deserves some attention and a lot of admiration.
I’m also pretty much a proponent of server side decorations for a very trivial reason:
Client side decorations make it sometimes near impossible to drag a window because the titlebar/headerbar is often so cluttered with hamburger menus, shashlik menus, chickennugget menus and buttons that there is no room left to place your pointer 
It all is, ofcourse, a matter of taste. One mans garbage is another mans treasure and I respect everyones choice in that because everyone has different demands from a desktop.
I guess my demands are somewhat unconventional.
And…oops, sorry for the long post. I think I got carried a bit away 
b.t.w. did you know that the real meaning of the word “classic” is “the best that a culture has to offer” ?
Have you come across any that are approaching the adaptability and malleability that you are looking for?
Below are references for those who don’t have a clue about workflow-oriented processes, and might want to explore what is out there. Sorry, but it is a vast sink-or-swim field. 
Group 1 Tools (infrastructure management)
Group 2 Tools (industrial scale)
Group 3 Tools (various workflow products and APIs)
I don’t use any of those tools. None of them are suitable in my line of work.