I may speak for myself here, but I find myself enjoying adult games far less than I used to.
I don't believe it has anything to do with lower quality games. I think it's more to do with my taste changing. The bubble which encapsles all the things I enjoy has slowly been shrinking. Bit by bit certain tags, kinks, and tropes have cropped up on my "No thanks" list.
In the past I didn't really care. As long as it wasn't scat or guro or something I'd play it. Yet now, the amount of games I enjoy has been decreasing. Even going back to play games I haven't touched in a couple of years which I know I enjoyed back then, leaves me with a sour taste in my mouth, or questioning why I ever liked that crap to begin with.
For me, it does feel like the quality of games is decreasing, however, I believe that it is more so me wanting to fit everything nicely into my little box of enjoyment, if it doesn't the game is trash to me.