Historically, US pornography has been regulated on the basis of whether or not it is obscene, defined by various Supreme Court tests over the years.

If it is not obscene, it's afforded First Amendment protections and allowed.

If it is obscene, it can be regulated by various entities, should they choose to do so.

Since the mid-70s(?), the Miller test [0] has been used.

Parent is pointing out that the Internet effectively obliterated the technical ability of various government entities to impose restrictions of any sort on obscene material, and consequently there's been essentially no regulation of internationally-based pornographic content since the 90s.

[0] https://en.m.wikipedia.org/wiki/Miller_test

Well, as an example, in the UK we had fairly tight control of pornographic material. Soft porn magazines were top shelf only. Movies had age ratings.

I'm not that old and I remember the controversy when someone found a sex game in GTA: San Andreas _if you hacked the game_.

Nowadays a kid with a smartphone googles and there you are, AI generated hardcore porn with your classmate's face. Different world.

Obscenity regulations are laws that censor the creation or distribution of creative works considered to be obscene, eg show a woman's ankle, or acknowledge that sex acts exist.