Regarding YouTube specifically: bandwidth is still an issue. It's nontrivial to stand up a service that can provide storage and reliable streaming of video, and

Regarding YouTube specifically: bandwidth is still an issue. It's nontrivial to stand up a service that can provide storage and reliable streaming of video, and the costs impact directly upon the provider. So it's an ecosystem where competition is risky (and if someone succeeds too well, Alphabet can just buy and squash them).