twit thread from a former google engineer who worked on the youtube recommendation system: https://twitter.com/gchaslot/status/1094359564559044610

the recommendation engine is designed to maximise watch time and nothing else

its model is weighted towards the preferences of users who spend the most time on the site

the reason youtube recommendations are turning people into conspiracy theorists, flat earthers and nazis is because conspiracy theorists, flat earthers and nazis spend all their time watching youtube