The art engine itself is literally a game. Honey Select and Koikatsu Party, you can find them on steam. They have a great character design engine, very cheap, hardware-vise, so developers who low in cash (to afford a graphic station to work with the engines like DAZ3D studio) love it (and actually it's they only choice). But HS/KK developer never allowed to use it's intellectual property for other devs.
And that's the case games with such an art will never allowed at steam. A pity.