The problem is Gnome seemed to look at mobile and "pre-sabotage" itself. Both Gnome 3 and Unbuntu Unity wound-up creating "tablet/mobile ready" shells when no one was going to be using them that way. Tablets only seemed to be the wave of the future because they were new and everyone was buying them. It only became evident later that laptops were going stick around for a while and be what most people still used if they were doing "real work".
But with the narrative being "this is the future", they were more or less pressured into it. The designers as well as programmers are volunteers and I would imagine designers want to work on the "cutting edge" even if that cutting edge is a complete disaster for users (just Microsoft's redesigned UI was).
Their target wasn't just tablets, but any device with a touchscreen and/or a small screen. As a Netbook user, I loved Unity and was excited about the Gnome 3 shell. It seemed like the logical progression of Ubuntu Netbook Remix.
What changed is that display and battery technology got better. I went from carrying around a tiny PC with an undersized keyboard (remember the Eee PC?) to one that weighs less, has a full size keyboard, and sports a display larger than the one the came with my first desktop computer. On this hardware, a traditional desktop environment feels cozy, while Gnome Shell feels foreign.
I owned one of the later models of the Asus EeePC and let me tell you, Gnome 3 ran like a old dog on it. Totally unusable. I don't know how you could use it. The processor was awful, the screen resolution tiny, while Gnome was a CPU hog and wasted screen space the eeepc simply didn't have with spacial bloat of interfaces evidently designed to be fat fingered on touch screens the eeepc didn't have.
But with the narrative being "this is the future", they were more or less pressured into it. The designers as well as programmers are volunteers and I would imagine designers want to work on the "cutting edge" even if that cutting edge is a complete disaster for users (just Microsoft's redesigned UI was).