Steam adopts a zero tolerance policy for some content and has no appeals process after adult games have been rejected under these terms. While steam is more than happy to profit off adult games they're absolutely not going to risk any scrutiny regarding anything that even sneezes in the same room as the age of consent. Developer's last game, MIST, featured a petite, adult woman which was enough for them to say, 'no.' More famously, the Muvluv franchise was ported using the all-ages edition, and Katawa Shoujo had it's adult content pruned from the steam release.
While there's some subtext about corruption within Steam's approval process- you can get away with pushing the envelope way harder as long as your politics are correct and it's pushing the boundary under the correct context- and heavily favoring certain developers, and especially favoring certain *western* developers but the basic premise makes sense. Valve wants money, Valve doesn't want money that even remotely risks them getting entangled with moral purity police who will label them pdf files.
Any hero out there ?
It's been a week since the update dropped, I guess.
It costs a whole ten bucks on itch.io. The developer has an established track record of finishing projects.