The problem that YouTube solves isn't simply delivering video content. People could make videos available for download long before YouTube existed, yet YouTube still quickly rose to prominence.
People use YouTube because it aggregates content for people in channels, makes engaging with videos and their creators easy, makes discovery easy for users through search and suggestions and allows people to roughly measure notability and quality of videos through up/down votes, views, and a creator's channel subs. They make becoming a content creator as easy as making an account and hitting upload. They make monetizing that content as easy as hitting a checkbox.
Similarly, people could get around the privacy concerns and constrictions of big social media sites by having a self-hosted blog or something along those lines... but we all know that the chance of someone— even someone you care about— breaking the comfort of their daily digi-routine to visit your site and comment on your happenings is pretty much nil. If all of their "friends" did it, then the whole ecosystem... well it wouldn't be an ecosystem anymore.