I have a hard time believing an organization like Google doesn't have the resources to provide a search engine that's just as usable as what they had 6 years ago (around the time I feel like the decay really set in). Seems a lot more likely that it's just more profitable to serve up garbage sponsored content.
I’d rather see a world with numerous paid/subscription search engines, that are motivated to do nothing but return search results well. I expect you would see some of the SEO crap getting solved.
On the other hand, they can achieve virtually the same outcome while keeping plausible deniability by just not doing anything that would downrank sites with ads (of which a significant chunk is likely to be Google's).
Spam sites often include ads.
Therefore the safest option is to never openly discuss it or intentionally do it and instead use other means to achieve the objective (don't intentionally rank spam higher, just defund/cancel any projects that would make it rank lower).
Yup, and I think we've seen how careless and thoughtless Google is, as an organization, with internal comms in the Epic case. It would be shocking if it hadn't been discovered in that, or a prior, lawsuit.