It's not.
If Disney was actually so concerned about reducing operating costs that they were willing to operate rides at reduced capacity you wouldn't see expensive installations like Tower of Terror, Everest, and the Magic Kingdom's various Mountains operating as fast as they can run them from the first half hour the park opens and even into the evenings before the park closes, when when fastpass returns are a non-issue. Ops gets as many people through these attractions as many times as possible as Ops can manage given the technical limitations of the ride hardware, all day, every day.
To argue otherwise is demonstrably false.