There's a great talk by Anil Dash that I like titled "The Web We Lost" that centers around on this topic - https://anildash.com/2012/12/13/the_web_we_lost/
Of all the companies in the world google will be the last to employ real humans to verify anything. Look online for the shear amount of forum threads full of people disgrunted with the their poor support response and lack of humans in the loop.
And Google already has a pretty good metric in the bounce rate without the need to add a "flag" option. That is, if you go back to the search page shortly after clicking a link, that link is probably irrelevant. I guess that SEO spammers found a way around that.
If we forced spammers to make web pages attractive and informative to humans instead of crawlers we’d be in a much better place
Google is super rich, they probably can if they want to dedicate a huge amount of resources to that. It is hard for humans to win against bots in this game.
> If we forced spammers to make web pages attractive and informative to humans instead of crawlers we’d be in a much better place
It is something spammers do. They make the page attractive using psychological tricks (like typical clickbait). They make it informative by copying parts of Wikipedia or StackOverflow. It does not make the world a better place, and it is something Google fights against, with mixed success.
And, yes, allow the user to permanently filter out domains from their search results.
But a small, boutique search engine where every account is a paying account, does not have this problem and can do it. And guess what - we are doing it. (Kagi)