I think it was a long time ago now, back when Google stopped improving their core service (search) to help profits through a better service than the rest and no longer "breaking markets" like introducing Gmail with seemingly infinite storage at the time... (another service that has stalled) And now instead rather going for squeezing out profits by keeping people on their sites and selling their data.
But maybe it was just a realization of what was more profitable? R&D becomes exponentially more expensive the more advanced search you try to provide, but any random weird company will be interested in user data for marketing.
Just a little anecdote: I have subscribed to a lot of newsletters about some FOSS projects I like. I use to never read those letters and now I have reached the limit. Now I can not delete those newsletters without deleting everything because I can not mark more than few tens of those letters at once while having few millions of them.
But maybe it was just a realization of what was more profitable? R&D becomes exponentially more expensive the more advanced search you try to provide, but any random weird company will be interested in user data for marketing.