then declined as sponsored results and SEO degraded things

In the 2000s, everything was open because of the ad driven model. Then ad blockers, mobile subscription model, and the dominance of a few apps such as Instagram and Youtube sucking up all the ad revenue made having an open web unsustainable.

How many Hacker News style open forums are left? Most open forums are dead because discussions happen on login platforms like Reddit, Facebook, Instagram, X, Discord, etc. The only reason HN is alive is because HN doesn't make need to make money. It's an ad for Y Combinator.

SEO only became an issue when all there is for crawlers is SEO content instead of true genuine content.

I seem to remember very few ads on the early web. Most sites I frequented were run by volunteers who paid out of their own pockets for webspace.