You don’t give Google enough credit: They totally can add a “report spam site” action in the search results, but they don’t, because they don’t care. It would help immensely to have websites disappear from search after 100 trusted Google users complain about them (after manual review). This stuff already exists and works on Google Maps.

Even the data collected from a personal blocklist would be useful for them, without explicitly reporting sites, but again they just don’t care.

They’ve been in the business of parsing websites for 25 years, surely they can tell ad-infested spam websites apart from good ones.

This is super useful: https://github.com/quenhus/uBlock-Origin-dev-filter

Removes sites that copy SO answers etc...

It is their fault when they've actively pressured real content into being indistinguishable from spam sites.

If you don't write like a drunk two year old and fill everything with key phrases now you simply don't appear in results, so any site that can become known has to be rewritten by gpt into barely intelligible garbage that dances around the point for four paragraphs when it could be communicated in four words..