This "progression" you speak of isn't progression. These AI devs are not pouring hard work and long hours into making AI games, and the artstyle aren't even theirs to begin with.
While I can't speak for everyone, in order to create a good consistent game with AI, it DOES take hard work and long hours. People are under the impression that AI does everything for you and requires very little work, while it does in fact take more work than Daz3D for example to set up scenes.
I'm talking about traditional Visual Novel style games. My New Girlfriend / Moonripple Lake as an example. I work together with them and we share a lot of tips and tricks with each other. The best way to visualize what I mean is the following:
With Daz3D, or HoneySelect, you have 100% control of what you want to create. There's no randomness involved at all. (The circle representing what you want to create
With AI, you get the following:
With the circle representing what you want to create, but the box showing all the possibilities AI will create. You can only do so much with prompting in order to reduce the size of the box, in order to get it really close to what you want, you need to use a lot of techniques which a lot of AI devs don't even know about, such as composing scenes in Photoshop, rendering the part in, and repeat that multiple times over and over. In the end, it'll be close, but it'll never be 1-1 with what you want to create due to the randomness involved.
I personally don't like these AI "Phone" games, as from a development perspective, they seem... lazy. A lot of those pictures are just one-off generations, with no coherent visual consistency that needs to be met at all times. While in a Visual novel, you do need that visual consistency. It's what sets the "greats" apart from the slop.