The easy monetization capability is unrivaled, this is a big reason people that make videos choose YouTube. This is where their network effects come from. People don't really choose where to watch videos, people choose where to upload them though.
But as far as a viewer is concerned, do you care what video host a video is on before you watch it? Probably not. You'll click a vimeo or dailymotion or whatever link if the video you want to watch is on one of those sites. YouTube by and large is not a social platform, so it's network effects are very limited.
IMO the reasons YouTube has basically a monopoly is they have what amounts to embedded google search that only searches their site, and their app comes preinstalled on almost all mobile phones. Think about it, as a user, you want to search for a video, you click the video searching app on your phone, oh it only searches YouTube? Oh well, the video is probably on YouTube anyway.