The recommendation engine was intentionally crippled because it was radicalizing people who were into conspiracy theories, militias, terroristic acts, etc. It sucks but I assume there's some work being done to get a new engine out without sending people down a rabbit hole.
For that I actually have a nice observation:
I always clear my cookies and website data on browser quit, and never login into Youtube. Which means I get a pretty vanilla "recommendation" experience, additional tracking attempts from Google put aside.
Visiting youtube, I could swear that the recommendations Youtube is trying to shove my way only change after several weeks or sometimes even months, it is always the same 8 videos on top of the front page for very long periods.
It starts to get somewhat relevant after I watch something, but then it looks like their recommendation engine does nothing more than "Recommend to user x the n most popular videos of roughly the same category as the last video user x watched" with a little bit of shuffling 1-3 videos from a larger set between those, sometimes, and that appears to be it.
