I would totally agree with you BUT - they make money on food, beverage, shopping. Those dollars would decrease with less guests AND may decrease among those to make up the cost of going. Disney can't reduce the numbers coming in too much without losing. Just like the Disney Resort guests are not enough to support the parks, there are actually more coming in from offsite than onsite and they are very important to profits.
Somewhere there is a balance they just are blind to. Everything worked well with FP+, everything seemed to work well last summer with just SB (not sure of attendance numbers) and everything worked way better before park reservations. We were shocked how packed AK was yesterday - never seen that, all day long. Well, a CM friend says it is the reservation system, DHS and MK were not open so folks go there and then hop. AK is a park not used to that many people and the rides are not sufficient if folks don't want to wander the trails etc. plus Lion King is the only show.