legal reasons. The default disclaimer is nonsense, it is hard to find an employer willing to sign a sensible disclaimer, and even when you have a nice employer it can still take months (years?) to get things through the FSF.
If it takes a long time, please contact r...@gnu.org or ass...@gnu.org. The disclaimers are legally necessary though, the FSF needs a paper trail in the case your employer comes back and claims that they have copyright over a change.
