Ed’s piece on this is considered pretty authoritative. There was a very specific moment where they determined, concretely, ad placement > utility of search results. Combined with years of damage from encouraging SEO tactics…well, here we are. Sure maybe this was always going to be the outcome, but we do know the major decisions that directly lead to this result as it played out.

If you haven’t read it from start to finish you should. If you have, what about it is insufficient?