Simply put, he's just not that good.
WWE used him plenty when he was at his height of popularity, and we all saw his popularity face as he was overexposed. While his shtick worked well on scripted, rehearsed, and most importantly well edited YouTube videos...TV, not so much.
It's awesome the way he used the Internet to get himself over, don't get me wrong, but in the end it may have been the worst thing that could've happened to him. If they could've built him up slowly and let him find his proper place in the mid card, maybe he could've carved out a Santino type role. But getting so over, so much more over than he shoud've been, and then having his credibility destroyed when people realized he wasn't as good as they thought...it's tough to recover from something like that, unfortunately.