On the other hand, managing a monetization platform (subscription billing, customer support, linking posts to email to social media notifications) is more complex than self-hosting. Not impossible, but more than most writers would want to take on themselves.
I think the fact that YT hosts video makes it quite a different beast from Medium. Self hosting video is still quite difficult, and expensive. Hosting text is much cheaper and simpler.
This fact changes the game quite a bit.