> Other services (e.g. YouTube Premium) reduce ads, but do not eliminate them, no matter how much you pay.

Hmm curious to know where you live that you still get Youtube-supplied ads with YT Premium?

Because "ad-free" is literally the headline feature.

Unless you're talking about in-video ads and sponsorships added in by the video creators themselves, and then that's not something in YT's control (although they provide the "skip commonly skipped sections" feature in Premium that helps with this).