YouTube is the main service because as every other alternative platform (such as ZippCast) realized, you cannot keep up with the server demands unless you're a billionaire. Uploading and watching videos requires an ungodly amount of server space as even forum owners in the 2000s found out, and it's just not possible for any Tom, Dick or Harry to do the same unless they've got an 8 - 9 digit net worth at the absolute lowest.

Also fun fact: The founder of ZippCast, Louis Gualtieri, trooned out.