I have a tendency to rewatch videos over and over, or rather, replay them because they make for good not-too-distracting background noise (I do the same with “The Big Lebowski”). Nearly my entire recommendations feed is videos I’ve seen a dozen times or more, and because I often visit YouTube to just quickly find something for background noise, I’ll just click whatever’s near the top. And next time I visit YouTube...those videos are at the top again.

That’s kind of annoying to me but I figured that it’s a problem of my own making. But it sounds like the algorithm behaves this way for other users who aren’t as weirdly repetitive as me?

I suspect this is fundamentally the same as Amazon recommending things you've already bought. Even if the likelihood of rewatching/repurchasing is small, that probability must compare favourably to the chance that their algorithm will select a 'correct' unseen item to display.

Recommendations are hard.

One of my cynical hypotheses is that, for videos that I'm rewatching for the nth time, the amount of energy/desire to interact is diminished (i.e. "vegging out"). Which is inversely proportional to the frequency that I'll click the "Skip Ad" buttons.

inject(tempermonkey/ublock/stylish etc) those two styles to at least be able to quickly spot visited links, mod color according to own preferences

    injectStyle('#watch7-sidebar .video-list-item a:visited .title {color: #141761;}');
    injectStyle('a.yt-uix-sessionlink:visited {color: #141761 !important;}');