Because that has been tried so many times over the decades.
The good sites put effort in to curate their ads and make sure they are things their audiences would enjoy. Lots of webcomics STILL have blog posts about doing this. Same with one of the more popular “steam deck” websites.
The problem is that this doesn’t work. Because people don’t permitlist those sites. They just block everything for the exact same reasons “I pirate it and if I like it I’ll buy it” was always a blatant lie for the vast majority of people (and no, I don’t care who consider themselves exceptions to that).
So when curated and “good” ads have almost zero benefit over shitty and obnoxious ones? The focus stops being “let’s serve good ads and trust our users to have our backs” and more “What can we do to actually get ANY ad revenue out of this so that we can keep the lights on?”