Youtubers take a 55% cut of ad revenue, which is about 1.8 cents per view. Youtube takes a 45% cut, but part of that is to subsidize the videos that currently don't have ads, so let's say 20% of current ad revenue is a reasonble price of Youtube removing ads from a single video.

For a video viewed a million times, it would cost a creator $6545 (.018 x 20/55 x 1,000,000) to keep the video ad free. I can't imagine anyone willing to pay that much to keep their videos ad-free.