Accessibility, usability, scalability at very, very large scale, actual searchability, and actual return on investment, because some people actually get money from youtube?

Actually, peertube, depending on the instance and the popularity of the content, can be incredibly frustrating for a viewer. And it can be frustrating to the content creator. Some people are quick to dismiss minor (and less minor) annoyances, are able to look for fixes, and so on, but for almost everyone? The experience is nightmareish, with incertain returns (or no returns at all, as it stands).

Once you fix all that, you might have a chance to convince larger entities to move to peertube. Well, more realistically, to host their own instance. Well, more realistically, to host multiple instances, because really some people would hammer the platform down with each video. See the issue yet?