They used to be one of the best simulation H game makers, with games like sexybeach, artificial girl being really successful and huge as people thought illusion is going to make the best "open" world H simulator. It's later around the mid 201x it felt like they kinda stop innovating. Honey select onwards alot of their games are just reused content even till now as we can see HC is just a mix match of systems between 2 games (Koikatsu's char maker + honey select gameplay). Even back when A.I shoujo was out, their advertising was rather misleading as we thought they are dabbling into actual machine learning A.I which the characters will "learn" and adapt to our playstyle which isn't true at all.
I've read people saying it's due to older staffs already leaving the company, which makes sense. illusion is suffering the same state as activision blizzard where old exployees who know what they want to create leaving the company. It's now just a shell that keeps reusing content and pump out games for sales.
I would rather they learn from KISS / CM3D and keep updating that 1 game and sell DLCs, at least the game that has a decent base gets more content as compared to them keep restarting games from "scratch" that provides nothing new.