Because to much nudity will cause the game's rating to go higher than it's basically Teen rating atm... which will cause overprotective mothers to not allow their kids to play it, and these games desperately want kids to play them. The entire goal of mtx is to separate fools from their money, and kids are the largest demographic of fools ever.
You start to see this in a lot of places. Fools are always in the majority and much more willing to toss their money away, so naturally everything tends to revolve around attracting them.. which just ruins it for everyone else. Take YouTube for example. Obvious clickbait videos with nothing of substance are all the rage these days with nothing more than the same formulaic baity thumbnails and titles.