I believe because they think they didn't have too! For whatever reason they are looking at some margin sales thingy. I think the would do quite well if they lowered the price.
Interestingly, today they announced their 'Spring Bundle' Xbox 360S 250gb, and Darksiders 2, and Arkan Asylum Digital. Still no price cut. They have even had 320gb hard drive in some of the other packages.
I find it funny how Microsoft is so risky and conservative at the same time.
Info: http://majornelson.com/2013/02/28/xbox-360-250gb-spring-value-bundle/







