I assumed it’s probably due to some creators becoming, or later being discovered as, “problematic” and/or some sort of brand risk. It would look more strange to unlist a few of them, so better to unlist all of them.

To be clear: This is speculation based on zero information 🙃. Just a total guess based on how things tend to go between internet culture and corporations. I’m probably wrong. It would be cool if YouTube would communicate things like this.

It’s unfortunate to see such cultural history hidden away. Though, tbh, this is probably the most that I’ve ever thought about YouTube Rewind, and I haven’t thought about it in many years.