Because every distributor of porn will always follow those rules?
They don’t have to follow the rules. The internet can and will police itself if it is made necessary.
Organizations that want to voluntarily police the internet should be able to make complaints to ICANN who then change the websites domain to the xxx extension (if available) and un-register the dot com, freeing it for resale.
Eventually it will sort it out with soft core dot coms serving as portals to hardcore dot x’s.
Parents can easily get their ISPs and phone providers to block the 3x extension.
You won’t get rid of porn, but you can dial back the intensity and reduce access to children.