I'm just not convinced anything is actually happening in baseball "ups and downs" (barring injuries or losing players, some anomalous situation). I played through high school and it all seemed quite random, unlike basketball where chemistry was key and led to peaks and valleys. Baseball can be decided by one swing or pitch...the margins are so small...which is why baseball teams have double digit losses every year and no one ever goes undefeated nor comes close.
All sports have variance, but I'm not convinced something is really happening teamwide on most occasions. Teams still go "cold" and "hot" as we perceive it as humans, but it's unlikely from some source of the team as a whole failing to be as good as they once were. I'd guess it's more of regular variance.