>>283480319 (OP)
Probably a combination of VNs losing popularity in general and the format being hard to adapt into an anime, or even a manga frankly.
VNs losing popularity is a bunch of factors, but I kinda suspect it has to do with their was association with sex in a world that dislikes explicit eroticism, them being confined to PC during the Dark Ages of PC Gaming, and VNs not being easy to promote through cross-media collaboration (through adaptation to manga and anime) when that's like 50% of how Japan does advertising. All these kinda kept VNs as niche and kept them from gaining enough popularity to stay in the limelight when the world changed.
But maybe I'm misunderstanding stuff since I'm not privy to what troubles Japanese VN developers. Maybe their problems are actually completely different.