I bet a big part of this was microsoft, once you make a deal to develop a game with them they get a lot of control over you in the contract. They tell you when they want the game out and ready to go, among other things.
I remember when gears of war came out. The developers had wanted to put out map packs to its players for no cost, just a free download as a thank you to its fans. Microsoft stepped in and blocked them from doing so.
So I am guessing the crysis people had to prioritize work load to make sure they made deadline. Knowing they could finish work on DX11 compatibility after release.