Is it the weight of the bigger Pro that pushes people to the 9.7 or dimensions? Both? We're used to taking laptops around so it's funny to see how the 12.9 is almost described as some sort of oversized monster when it's 1kg with the ASK connected.
How much moving around does one actually do? I'm usually sat at a desk or on the sofa with it on my lap. It sounds like some of you are constantly roaming and can't hold it! I actually do this no problem with the bigger 12.9 Pro when I use it as a mobile whiteboard that Air plays back to my Apple TV on a big screen. I don't even bother snapping off the keyboard either.
Volume for me. The 12.9" iPad Pro takes up more room than my rMB. I still need a "real" laptop capable of running Windows so I keep the rMB around.