There are people who like running their own linux server with their own hardware. Occasionally those people are also interesting in creating videos or have friends/family that are.
There are also people who get funded through sites like patreon, who might not care too much for youtube advertisement or YT freemium. Sometimes you even see youtube personalities switching to twitch or other platforms just in order to escape youtube and do legal activity which is just close to impossible on youtube. There is an endless stream of youtube videos complaing about youtube copyright system and how it makes their job close to impossible in some cases. Game reviews and movie reviews are two areas almost dominated by the issue of false copyright claims, which has forced some creators to abandon the platform as a revenue sources.
There is even float plane which was designed from the ground to solve the youtube problem, created by a company that fully relied on youtube for its existence. If your company existence is depended on a free service provided by someone else, you might want to reconsider how safe you should feel. PeerTube might serve a similar purpose.
On top of that we have scientists who might want to know that their research isn't taken down because of false copyright claims or fleeting politics. A company that has linked instruction videos in their books/teaching material might want to be sure that links still work 10 years from now. Activists might want to avoid the risk that their documentation doesn't go dark from a political requests or false claim. Police brutality victims might want to be sure that the copyrighted music playing in the background, placed there intentionally to get copyright claims, does not stop them from uploading videos.