With mainline-supported cameras using a standard API, a userland application that does streaming and all kinds of neat stuff is just much more doable IMHO.
They're not the only project that builds a ton of userland stuff on top of a rotten kernel foundation: oe-alliance has nine distros downstream from it, and hundreds of supported hardware platforms. As far as I can tell it's all ancient vendor kernels with un-upstreamable drivers.