Let me guess... the people who sell them?
Never seen a good image coming out of a GoPro and its plastic lens. Great for holiday action videos yeah, serious filmmaking? Hell no.
The 4k BMD has many advantages over the other BMD cameras, Global Shutter, APS-C sensor and 4k are well worth losing 1 or 2 stops dynamic range, at least to me. People do great work with H264 DSLRs, you just have to know your camera and how to compensate for its weaknesses, and at that price range it should be the most capable camera around.
Personally, I will be thrilled to leave rolling shutter jello ridden cameras behind as soon as I can.