They did it for Verizon. Here's my reasoning:
Android 2.2 includes a free feature to turn the phone into a WAP. With Droid X, you can pay Verizon $20/month to do the same thing. Droid X starts out as Android 2.1 but will be updated to 2.2. I'm sure that its 2.2 will disable stock Android 2.2's free WAP feature, so as not to compete with the $20/month offering. If Motorola allowed modders to install a stock Android 2.2, Verizon might not make as much money off this new feature.