That's only because Southwest didn't have a schedule to modify. If they had released flights more than 6 or 7 months in advance, they'd have to make changes on the fly as well.

Frankly, the schedule changes that "legacies" make doesn't really bother anyone. It's a fact of life and most legacy travelers don't mind because at least we know we have a reservation made in the system. Plus, about 90% of the changes are 30 minutes one way or the other... and several are simply flight number changes with nothing affecting the flight times.