I think that Google's monopoly and their worldview that everything is data to be mined has created a feedback loop that killed the web of old.
The web was originally very social in nature. By linking to another page you spent some social currency to lift up others who were worthy. You, the other author and the audience all understood the social contract enshrined in a link. Google rejected that model and successfully changed the web to be a place where Google simply directed people to their final destination.
SEO became first possible and then necessary. The audience for hobbyists and anyone who can't pour money into optimising their Google results has dried up. The nature of Google search results undermines whatever opportunity the author had to build a relationship with their audience. Google reminds you that this is all an impersonal transaction: this page has the recipe you want, it lets you buy a product, or it answers your question. The value of this connection can by quantified as unique visitors, bounce rate and time on page.
Intertwined webs of relationships between pages have been replaced by a graph where the only edge that matters is the one that connects you to Google.
With the social dimension of the web undermined, and the audience siphoned off to the big, commercial, operations, it makes sense that creators migrate to platforms that will give them an audience. It is not that Google results are getting worse, it's that Google has accidentally killed the web as a source of valuable data for them to mine.