Probably the fact that this is a hard problem. Seriously, hundreds if not thousands of people are working on creating tools for animators, for 3D software companies, movie and game studios. If it was easy, it would have been solved by now.
If we look at Brett Victors inspirational videos the one thing I can take away is "Change the game". If we play the same game as before things wont change much. So, creating animations is a hard problem to solve. But, can someone change the game ? For centuries, extracting aluminium out of its alloy was a hard problem, or extracting mica. Once it was done, it changed the game.
What am I currently using? 3D Studio Max. (and Motionbuilder, and some high-end mocap technology, and a lot of outsourcing.)
Seriously, it's a hard problem. I'm not saying "don't try", but it's a hard problem.
It's by for the most interesting development for animation that I've seen for years. In about an hour I was able to produce 15 sec of reasonable good animation the first time I used it.
Their process is more akin to Photoshop than anything else as it's a destructive process rather than procedural.
I found it quite enlightening.