To understand this problem, you have to first see how JustinTV came and left. How youtube became #1 and since then never had a challenger.
Hint 1 : Google and capital.
JustinTV started out as a joke and publicity stunt, then they became a troll channel competing with youtube and cam girls with porn.
What about UStream, Vimeo and Podshow? Long story for each, but Vimeo came closest to Youtube, largely due to video resolution and graphic UI.
Podshow sucked up mevio (yes, that’s a real name).
Don’t even get me started on soundcloud, bandcamp and last.fm.
Then there’s libsyn, podbean, podcastpickle, and loomia. The list might never end, but I think you see the pattern. Sites die, and not even wayback machine can keep them up fast enough.