I think someone once told me its about charge backs. People will pay up for hours and hours of content (more for addicts) and then issue a chargeback, or otherwise say their card was stolen (how dare you insinuate I'm into that fetish! Type shit) and because there is no physical product to seize, the company is left with repeatedly eating investigation costs into fraudulent porn addicts.
E: I'm not judging anyone's porn content, idgaf what you smack or flick to. Merely an observation of people not realizing how much they will charge their CC until statement time, and freak out and then chargeback.
Microsoft owns Guitar Hero
Harmonix owns Rock Band. And Epic Games owns Harmonix. Fortnite Festival is (unfortunately) the spiritual successor you mentioned, except you gotta buy every song because of course. (Free players have 5 tracks they get to do for free but if you want a decent library you gotta start buying em from the shop)
Clone Hero is the alternative