Really a lot of the problems with why you don't see a lot of expansion games in general is because expansion as both a concept and a fetish is really draining on resources, speaking as someone who's tried and failed to help make assets for a game, uh, twice now, I think.
Example:
Say you have a VN, no expansion. It's early in development, so there's 2 CGs and five outfits. That's ten fully-detailed images you have to hire an artist for (or if you're cheap, 2 images but edited into 10 total.)
Now imagine said game is actually an expansion game.
Two bust sizes, you're already up to 20 images total. Two bust sizes, two butt sizes, and a pregnancy alt? Oh god now you're doing MATH, your game has barely any content and you've already paid an artist to make, like, 80 images (or 80 edits, I guess) of all the different combinations the character could be in. (Also: sorry for the super lazy math, I'm sure I'm wrong.)
Between the money needed to hire an artist like that and the rapidly growing filesize, you're already doomed. Even then, a game with 2 CGs would suck, and an "expansion" game with only two bust sizes sucks too, so you're already getting critiqued for having no content despite already spending probably like $500-1000 on the game's assets.
(EDIT: forgot to mention, all these issues are why I strongly suggest that expansion, BE, inflation-whatever game devs should absolutely be working in 3D, not 2D, so that they can simply move sliders around to expand and shrink characters however they want in whatever combination they want.)
