Over-18 documentation technically is still required by the gov't and has since 1986 after the Tracy Lords debacle, but usually only actual production studios still follow it. These days most porn is made by independent stars like on OnlyFans and Pornhub (before the revamp there was bad PR that some of the channels were still high school students 15-16yo, some of which were there against their will working for a "pimp"), way too many of them for the gov't to police. Sure someone might get busted but that doesn't mean much when 10,000 others get away with it. As far as incest, it's not illegal everywhere with over 25 countries and 3 US states still fine with it (depending on circumstances, dads still can't legally fuck their daughters for example in those 3 states, but bro/sis is fine as long as it's consentual). Visa/MC in turn blame the gov't for putting pressure on them via the banking system for certain porn genres like incest, but that case was settled back in 2015 on First Amendment grounds (in essence gov't can't pressure private business to do it's censorship work for them, nor can Visa/MC webline certain adult-oriented businesses that otherwise qualify and are legal), but obviously it's still happening despite the court ruling.