Another aspect is the utterly strange way internal accounting is done at large companies. When you have lots of department heads trying to optimize for their departments local optima without incentive to consider the companies global optima, you often get seemingly irrational behavior.

Sometimes it simply makes sense for a department to spend a whole lot of money right now as opposed to a little each month, since when money is spent affects which budget it ends up on, which in turn affects things like bonuses and raises.