It is less about image quality but more about what you can do with the cameras. Smaller? 60fps? 120fps? 360°? AI? 40MP? 100MP? All of this _can_ be an argument to upgrade, even if image quality has improved zero.
The A7r2 can do 42MP. It's not really practical to have any more megapixels.
The rest of the things are useless to 99.9% of people, so it's just a gimmick or convenience update. That's where we're at for cameras.
Phones however still see big image quality improvements, and you could take pictures that were previously impossible as they added and improved suppmentary cameras.
We've already seen cameras running on Android. Eventually, we'll see cameras with all of the artificial image manipulation that you are seeing in the phones. I'm not so sure that's a good thing, but it will be done. At that point, it will be this annual update cycle
The A7r2 actually does run android. You can even sideload APKs. It does some level of image manipulation, if you ask it to. The issue is that photographers want to be in control of their image, so the generally use RAW files. Because of that, the artificial image manipulation is left to your computer for best results (I often use the new AI features of Lightroom, they're great)
The image quality of phones still improves a lot every year, though they are approaching their limit.