I suspect it has more to do with the decline of visual novels as a medium them with the difficulty of adapting them (though everything you're saying in that regard is obviously true).

The golden age of visual novels that was the early 2000s is over. Total sales for visual novels are a fraction of what they used to be. Many premium visual novel developers have been forced to shut doors, and the ones that are left now are all relics of the golden age, producing rehash after rehash of the same formula that made them popular 10 years ago.

Look up a recent list of "kamige" (lit. god games, i.e. must read games) and you'll hardly find anything made within the last 5 years. It's pretty telling that even the game you named as am example of a recent vn anime, muv luv, originally came out 16 (!) years ago.

Can't make a good anime adaption if there are no good games to adapt. It's all light novels now.

(Oh and fun bonus fact: People love to blame the recent deluge of isekai anime on one popular series or another. The truth is, isekai has always been an extremely popular light novel genre. The real reason why you're seeing so many isekai anime right now is that light novels are the easiest and most popular medium to adapt into late night anime.)