Why not just have everything at Cape Canaveral? And why the hell is Mission Control in Houston, TX, of all places? Would I be wrong in thinking that Lyndon Johnson had a big part in this?
Politics.
Back in the Sixties, it was determined that it woud be more efficient for the actual mission control functions to be in a seperate building from the launch control functions. It was purely pork for the “seperate facility” to be constructed in another state rather than just down the road from the Cape.
For one thing, all of the simulators are located in Houston, so were something to go wrong, the engineers trying to solve the problem in the simulator would be in direct contact with the Shuttle, instead of having to patch through to the Kennedy Space Center and then to the shuttle.
Didn’t someone manage to slip a rider into some bill requiring that the launch and control facilities be in separate states ?
Why is mission control in Houston? Three letters explain it all.
LBJ Then the vice president of the US.
And what exactly is wrong with Houston, of all places? 
An earlier thread on this subject.