I think there is a small degree of complexity because you have to do the character design, and those games where they use sprites and CG have to do the clothing change in both.One can hope.
I will say that the game is impressive even without corruption based clothing progression.
For NTR RPGs, only RPGMaker VX Ace CircleKame games and Curse of Pleasure have this. No other dev has attempted it TMK. So I'm assuming there's quite a lot of complexity involved with it, especially with RPGMaker MV/MZ.
A lot of developers pay artists to do that and of course it's expensive. I understand that pixel art artists can charge you between 60$-90$ to make a complete design (I mean the model and its movement), while cg artists for the minimum can charge you up to 100$ to make an illustration, so it is understandable that not many want to make clothing changes, especially if they are small developers or do not have a lot of capital.
But I think Inatari didn't suffer for that because I think he does the illustrations and pixel models himself (I'm not 100% sure).
At least in HC, you can see a change in the clothes of the girls as you go along, and N_taii said that maybe he will ask the artist to do the illustrations of the girls with the different outfits we will see in the game.
There is also another game, I don't remember the name but it is an NTR about a fox girl, which has many changes of attire and they are seen both in the illustrations and in the pixel art model.