Um, let's not all forget that all of the titles the OP listed were made by Japanese devs. There've always been more Japanese-developed porn RPGs, so just by sheer weight of numbers they're going to have more well-developed games--they'll also have more garbage asset-flip-type games, although those are going to zonk out on DLSite and never get translated (theoretically). Also, the discussion and feedback that takes place on English language forums like this one really aren't going to affect what they're doing over there. So Western devs might be getting a message that RPG Maker isn't widely liked, but the Japanese are going to be driven by what sells on DLSite and Getchu (and I guess maybe Steam now?). I don't think they Patreon much.
I've actually noticed the same kind of trend, but I'm going to chalk it up either to coincidental burnout by prominent devs, or maybe flagging sales. VNs and what the Japanese call "adventure" games have always been the bulk of what lands on DLSite, I think, so we might just be seeing a correction back to what makes money without requiring a lot of novel programming effort.
I don't exactly have my finger on the pulse of the Japanese indie porn game industry, but I do know one or two things. Scale Garden, for one, went quiet a while ago. CircleKAME hit its wall some time ago and is in the midst of the episodic game death spiral with their new one. Black Panda came out with a new game a little while ago, and instead of a moderate-length RPG with a bunch of scenes and combat sex, it's some silly low-effort roguelite thing made in MV with something like 12 scenes. Acerola's made the same two games with different themes something like three times now, and I don't know if they're still making money doing it or not. I haven't noticed too many breakout new devs, either.
For another thing, RPG Maker MV's been out for a while now, and you still see a surprising number of games developed in VX Ace--I don't have a basis for saying it, but I'm guessing the Japanese dev community hasn't really bought into MV, or is getting to the point where they can't expand it any longer. Wolf RPG hasn't changed, I don't think, in I-don't-know-how-many versions/
It's also possible that the Japanese players are getting tired of RPGs. I get this feeling that innovative use of the engine is just as important over there as porn content, and innovating takes time and effort that those devs might just be running out of. I don't know how much profit the average Meltys Quest or whatever clears. Like I mentioned up there, time and money spent on adding stuff to MV is time and money that could've been spent drawing porn.
Anyhow, I only follow the market as a porn consumer, so these aren't systematic or professional industry assessments. It's wild guessing mixed with anecdotes, which frankly is about the best a person can expect on a porn forum. No offense.