GPU improvement rate does not look to be stalling. Nvidia is still introducing impressive new features (support for HW accelerated ray-tracing, NN acceleration for stuff like DLSS, etc.) while steadily improving performance. It's just getting harder to make games look nicer, because they already look really nice. Artists/Graphics devs have learned to do really impressive things using just rasterization. As someone who is interested in GPU programming, ML and rendering, I personally find it really impressive what Nvidia has been doing over the last couple of years.
Though I have to say, for all its faults, CP2077 really blew me away graphically (using the RTX support) like no other game did so far. Also, VR would also really benefit from better GPUs. And 4K gaming is also not quite there yet. So actually, I maybe wouldn't even say that. Performance improvements are still welcome.
The problem is more that there is an unprecedented demand for compute. ML, Crypto mining, Gaming being more popular than ever with Corona, etc. just means that demand is higher than ever. Combine that with the new console launch and exhausted semiconductor manufacturing capabilities and you can easily see why customers are biting the bullet and going for less pricy, older cards.