Why did Kennedy have four control rooms but Houston had only two?

Question

Kennedy Space Center has four firing control rooms, one for each bay in the Vehicle Assembly Building.

After launch, authority was transferred to the mission control center in Houston. For the entire Apollo program and about half of the Shuttle program, there were only two control rooms in Houston. (Two more became operational in 1998, but that is not the scope of this question.)

Why was KSC built with more control rooms than Houston? If there was the possibility of having four spacecraft at Kennedy, one would expect Houston to have the capacity to control all of them.

Answer 1

Moonport says

4 firing rooms, one for each of the high bays in the VAB.

but

The original plan called for four rectangular firing rooms, 28 by 46 meters; one was never to be equipped.

i.e. to support the original Apollo flight rate projections.

The firing rooms were used for prelaunch checkout of the vehicles so they could have had several in that state. Houston needed fewer because simultaneous flight operations of more than one mission weren't planned (with the short-duration exception of Skylab + transfer vehicle).