Honestly the biggest failing is just SEO spam sites got too good at defeating the algorithm. The amount of bloody listicles or quora nonsense or backlink farming websties that come up in search is crazy.
The funny thing is that it seems like when they gave up it wasn't because some new advancement in the arms race. It was well before LLMs hit the scene. The SEO spam was still incredibly obvious to a human reader. Really seems like some data-driven approach demonstrated that surrendering on this front led to increased ad revenue.
Problem is that no mainstream search engine will do it because they happen to also be in the ad business and wouldn't want to reduce their own revenue stream.
Though maybe it's a long term gain. I know many normal (i.e. non-IT) people who've noticed the poor search results, yet they continue to use Google search.