I think it’s mostly the average quality of the information available has regressed.
I’m fairly certain they’re doing the best they can with what’s available to them, but right now they probably get more accurate results by focusing on what is popular than by blindly accepting the contents of the websites.
That goes back to them upranking fresher results. If the old results were better, they should keep them at the top and ignore fresher but worse quality content. Google exists to rank content, and it should be by quality not age.
I’m fairly certain they’re doing the best they can with what’s available to them, but right now they probably get more accurate results by focusing on what is popular than by blindly accepting the contents of the websites.