> But to remove public dislikes across the entire site takes away a valuable indicator of video quality.
Indeed. Which means you'd have to watch the ads (oh, right, there's also a video involved) to determine that the content was garbage.
If you can tell without watching a video that it's trash, you might not watch it - which is opposed to YouTube's goal of increasing total video hours watched. Or, at least, their short term goal of making sure people watch stuff (I suspect the long term effects of making people watch more low grade nonsense won't show up in this quarter's growth numbers, which means it's Someone Else's Problem - get promoted and go do something else, it's the Google Way).
Despite all the claims from Google and YouTube about how they're trying to promote certain content and reduce exposure to others, it's a reasonable bet that their algorithms still don't understand much of anything about a video beyond "Oh, hey, people who watch this video watch more related videos later, so the more people I show it to, the more those people will watch, which increases hours watched!"
So, presumably, "dislikes" interfered with people watching more video. Remove the dislikes, problem solved. At least for their definition of "problem" and "solved."