Why? Porn in magazine or movie form used to be age-restricted. Assume for a moment that was the correct, or at least a reasonable and permissible policy.
Why should it suddenly not be the appropriate policy, only because it's on the internet? Why do you say that laws do not or should not apply when you sprinkle a bit of "internet" over it?
It reminds me of the crypto-bro argument that, don't know, money laundering and tax evasion and offering securities without appropriate disclosure is illegal and tightly regulated, but if you do it with "blockchain", then it is perfectly fine. What sort of mindset is that?