There is one legitimate reason for such a clause. If you are going to try and yank the rug out from under everyone by revoking OGL 1.0a, then you also put in a bunch of other ridiculous changes so that when you get pushback, you can "compromise" by removing those, leaving you with the change or changes you wanted to begin with. You get what you wanted and the customers feel like that got something out of it.
WotC just failed to anticipate the level of pushback they would get and continue to make things worse with their deceptive practices.