Mobile devices are very constrained. The OSes are locked down, the screens are small, high CPU apps are out, and input is slow and cumbersome.
After trying a lot of apps I have found that a smart phone has only a few functions:
1. Talking and texting.
2. Taking pictures and video.
3. Maps and directions.
4. Music, movies, ebooks.
5. Brief interactions with services like Uber, Lyft, AirBnB, Los Angeles metro, etc.
6. Casual web browsing. (I want a bigger screen and a keyboard for anything in depth.)
7. edit: Casual gaming.
Looking at how most other people use phones I don't think I am alone.
These devices are limited and I don't think it took us long to exhaust their potential. There just isn't much else a phone can do well (and that locked down vendor fiefdoms will allow).
The PC era on the other hand gave us a long, wide, and deep trench of innovation that is still not exhausted. PCs are more open, more extensible, and have a much wider IO path to the human in the chair. The breadth of what a PC can do is incredible.
(The main problem with PCs is antiquated, insecure, bloated operating systems. Fix that and I think you'd see even more innovation.)
Of course I have been a mobile skeptic since the iPhone. I just saw the next incarnation of the feature phone. Since it was still locked down by carriers and vendors and since its bandwidth to the user is poor I knew it would not deliver lasting innovation.