We actually do run a lot of high-low actions, though its obviously set within a broader, more modern offensive system rather than an exclusive staple. Those particular actions may look a little different than what people saw 10, 20, 30+ years ago because of that. Even in this short video of only a handful of offensive plays, you certainly see a few high-low actions.
As far as winning 6 games in a row in March --> April, only one team per season does this. Feel it is important to note that. So, no offensive system is infallible, and no matter what a team runs its fans will always have ideas (many times very good ones!) of how to improve or expand it.