Then there was the quality issue. VP8 Sucks. It sucks less now but it is still inferior to x264 encodes.
Then there were the cost benefits of converting to Vp8, no bandwidth saving, more storage cost, and other resources for converting its existing library of video FAR out weight the benefits of using a "not yet proven" patents free video which gives not quality or other improvement.
Dont get me wrong, I am not against Vp8 or Patents Free Video Codec. But i am just being realistic here. It is going to be hard, but at least Opus has proven you can actually create Best of Current Audio Codec and patents free. And Mozilla are already working Daala ( Code Name, and i Hope it remains as a code name only ) aims to have superior performance to h.265.