It's only partially based on history these days. The YouTube subreddit is ram packed with posts about the issue, it looks like 50% of your recommendations are relevent to you, the other half is randomly generated with seemingly nothing in place to at least try and match them up to your known interests.

It started approx 2 years ago and has gradually gotten worse to the point where some users see no recommendations relevent to them at all.

Don't take my word for it: https://old.reddit.com/r/youtube/search?q=recommendations&re...