I'm just surprised because it really does work for me. But, I make a point of never voting/subscribing/commenting/queuing/etc. And the difference between when I'm logged out and logged in is very stark.
In addition to curating what I want to see with upvotes/subscriptions, I also use the "Not interested" and "Don't recommend channel" buttons heavily. For some reason YouTube always recommends those stupid "meditation music" videos, even though I have never watched one and I always block those channels. Honestly, YouTube's recommendation engine is shite; even when I tell them exactly what I like, it still recommends absolute tripe, and most of what I discover comes from external (personal) recommendations.
If it starts recommending the same videos to me I press the Not Interestes button.