Maybe Apple was worried about the weight. Most people who saw the keynote probably noticed how they boasted about the iPad Pro being about the same thickness and weight as the original iPad 1.
When it comes to the iPhones I hate Apple's obsession with thinness (which usually also implies reduced weight), I want more battery life from my phone, but when it comes to the iPads I really do think that weight is still an issue except maybe for the Mini. I find that even with my Air 1 (which admittedly is slightly heavier than the Air 2) my thumb joint and upper knuckle joints in particular can get quite sore if I use if one-handed for maybe an hour or two non-stop. Unfortunately, despite the cumulative stress on my joints, I find one-handed use by far the most natural and convenient way to hold my iPad.
Going back to weight, look at what happened with the new 3D Touch enabled iPhones:
6s - volume up 4.12% vs the 6 but weight up 10.85% compared to the 6
6s+ - volume up 3.01% vs the 6+ but weight up 11.63% compared to the 6+
Admittedly the material and the thickness of the rear shells were changed to make them stronger but one guy who got hold of a leaked 6s rear shell did a video that included a weight comparison and according to his scales the 6s shell was actually slightly lighter than the old 6 shell so I suspect these disproportionate weight increases (i.e. increased average density) in the new iPhones are down to the addition of 3D Touch, probably particularly the haptic engine since it has actuators and weights in it.
My guess is that Apple wants to wait until there is another generation's worth of increased power efficiency for the SoC, radios & screen that would allow it to reduce the battery capacity to save enough weight to accommodate the haptic engine without making the device any heavier than it already is.