Well, that's not necessarily true. If the park has two trains and runs one of them, they'll save money by being able to use parts from their spare they already paid for, and not paying to order new parts.
Also, they're using power every time they run the lift motor, that power costs money. If they're only running one train they're running that lift less often, therefore saving money.
I also believe maybe the biggest factor is they actually want the lineup to take a long time. The longer people are in the park, the more tempting to spend money. With a smaller park with fewer coasters such as DL, they don't want you to be finished in a couple of hours and leave. My thoughts anyway.