You are missing, that many people in that space don't want to solve that specific problem
* Some companies and their lobbies want to sell their products for filtering or whatever
* Some people want to get rid of all sinful porn
* Some want to block a lot more content for more people and need infrastructure
* Some want to have further control
Etc. "protecting the children" is often a good way to denounce opponents
It really shouldn't be needed: web pages are all about tags with data and metadata. It shouldn't be hard to add metadata about content type.
I never quite understood why labeling initiatives never gained traction:
* https://en.wikipedia.org/wiki/Platform_for_Internet_Content_...
* https://www.w3.org/2007/powder/
Throw some <meta> tags in and browsers can parse: then have a password-protected "filter controls" area in settings (and perhaps a GPO for corporate environments).