2 Mb. Just because it's politically easier to implement. It'll buy us some time.
Time to implement something different, like lightning.

My favorite one - the solution that was suggested at the conference: introduce the second type of blocks that contain transactions only and issued 60 times more often, every 10 seconds or so. Those blocks are not for determining winner of reward, so they won't cause orphan problems. This solution will give us 60 times more space for transactions and reduce confirmation time 60-fold!  I think it is the perfect solution, even better than lightning, since it's not hub-based.