Valve has hundreds if not thousands of highly and expressly pornographic games on its platform, so I don't think this can be chalked up to the Collective Shout folks' spectre somehow looming over Valve. As another commenter pointed out, according to the devs' own timeline, Valve's rejection happened prior to the recent successful Collective Should payment-processor targeting.

I suspect that EGS and Humble probably halted sale at the last minute due to the added press naming them as distributors prior to launch, often in articles that included Valve's response asserting that it contained questionable content related to minors, and them going, "hey what? Hold on a sec, we don't know anything about that."

If you were about to sell a bunch of cars, and a major dealership announced they wouldn't sell them because their trunks were all full of cocaine, a couple days before launch, you'd probably delay your launch to double-check as well.

Unfortunately, the developers' own initial press statements where they sort of feigned innocence ignorance (after they had already changed the scene presumed to be in question, meaning they at least had some idea that was likely the issue) probably didn't help their credibility in other platforms' eyes, as far as being business partners goes.

Okay, cool. Do you think having a little girl talk to a naked horseman is something that would help sell the game? Or make it onto a marketplace anywhere? Thats why it was removed and they already tried to placate by makkng the girl an adult and that didnt work obviously. So whats your point here? Leave that content in the game? That doesnt solve the developers problem.