My theory is that once you've watched a few of the videos you're interested in, the YouTube algorithm curates a list for me which I can continue watching. I do not want to be notified or otherwise informed of every video a channel publishes.
I subscribe to 200+ channels, not because I want to see every video from all of them but because it generations a "Subscriptions" page full of content I know has already proven to be to my taste, because I find all the "front page" content on YouTube to be absolute crap.
YouTube has an incredible amount of legitimately interesting content but it's on smaller channels buried by clickbait/fake-drama/lowest-common-denominator stuff, so subscribing to the good channels you find is the only way to find the needles in the haystack.
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In keeping with the TRUE purpose of YouTube, instead of posting dozens of miscellaneous channel links, I'll offer the BEST purveyors of cat videos, who all happen to be Korean:
https://www.youtube.com/c/SuriNoel/videos