Of course I have an answer. To do something about the unlimited firehose of porn, violence, divisive, and addictive content that has been pointed at children for the past generation or so.

There's literally nothing confusing about the "why" in this discussion.

The fact that bad people use the "what about the children" argument regularly for bad reasons doesn't mean that all such arguments are bogus.

In fact, it's an indication of exactly the opposite, it's so regularly used because there is a broad consensus that we need to protect children from harm which is why it's often effective as an arguing tool.

The relevant frame for this discussion is will it actually work, and what are the tradeoffs. A trivially small amount of money for a simple age verification scheme isn't a particularly meaningful tradeoff against a genuine social problem. The bigger, more genuine issues are around privacy and censorship and I do in fact concede those are real.