It is believed that for the first time the behavioral factor began to be taken into account in Google back in 2003, when the Florida (now Panda) filter appeared. The search engine began to take user characteristics into account, which led to the sinking of many “dishonest” web resources.
A few years later, Microsoft (the creator of the Bing search engine) presented the Browserank technology (a PF accounting algorithm). It was supposed to become more loyal than Florida and Google's PageRank, since it would bring out portals with the highest user activity (clicks) to the TOP.
Now, when ranking, as before, the optimization of content and links is taken into account, but user characteristics are the main criterion.