Those are the people who will happily go to an alternative product. And while that product might start as a pirate YouTube, the one that nabs 30% of YT's traffic can certainly make a pivot to legit. If you're a content creator whose audience is mostly in that group, you're likely to start posting content directly on the competitor's site.
I'm guessing OP had their account banned for using a tool like yt-dl too aggressively. Then again, doing that does give a warning.
I explained exactly why I think they are important in that entire paragraph. And the evidence I'm right is the fact that YouTube could trivially prevent ad-blockers tomorrow, but they don't. They've tried it and quickly rolled back the changes. Presumably they lost a lot more audience than expected.