bash

It's because the FSF is the copyright holder in their own works. (Not the *sole* copyright holder, but their works are vastly more homogeneous in copyright ownership than the Linux kernel is.)

It is a long established principle that a copyright holder cannot violate the license in his/her/its own work.

Consequently, the copyright holder can distribute the "source" of a GPLed work of theirs in any form they wish, or not at all.

Red Hat is not in this position with respect to the Linux kernel.

Does that clear things up?

(I swear--people don't read my long posts, and don't understand the short ones.)