I am a clipper with a fairly modest channel (around 10k subs). Not the one in the OP, though. A lot of clipping channels have been getting hit with the "reused content" warning over the last few months - it's something automated by YouTube, not from Cover. It happens to Niji clippers, too. Vshojo and indie clippers seem to avoid it because the original content isn't on youtube, so the automation doesn't catch it.
Getting demonetized is demoralizing, but it's a bad sign if a clipper stops entirely because of it. I know when JShay (a Korone clipper/subber) got hit by the same issue a while back, he just kept uploading normally while trying to get the issue fixed. The ad revenue is nice, but the good clippers I know all do it out of love for their oshis. Some of the worst drama clippers are clearly in it for the views/money.
I originally did not want to monetize my channel at all, but I learned that YouTube would still put ads on my channel if I declined monetization. If you become a YT partner, you get extra control over the ads on your videos, so I'm able to disable mid-roll ads and unskippable ads for my viewers. The extra revenue is not that much (around $1 USD for every 1000 views) but it gives me extra spending money which I try to use on superchats, merch, or art commissions.
Another clipper I know says he declined monetization and thinks it's negatively affecting the algorithm's effect on his channel. I don't know if this is actually true, though.
Thanks for reading