YouTube got to where it is by making intentional moves to be the only game in town. They aren’t the most user-hostile platform by any means, but they have been coasting on the network effects of backlogged content for close to a decade now. Even if a competitor could deal with network and storage costs, and somehow manage to attract a network of uploaders, the platform would be 20 years behind, and there’s certain content (e.g. older content) that you simply wouldn’t ever be able to find there in any appreciable quantity.