Given that VP9 is in no way superior to H.264 [1][2], this is purely an ideological push to favor their own format over a more widely supported another, and is a clear detriment to users.
[1] http://www.streamingmedia.com/Articles/Editorial/Featured-Ar... [2] https://infoscience.epfl.ch/record/200925/files/article-vp9-... [3] https://news.ycombinator.com/item?id=13226309