the one thing that sticks in my mind is that the intencity building is right next to the parade entry, which essentially means big vehicles (like fire trucks and ambulances) would enter the park there.
The old first aid building was landlocked. there's no way to get a patient out of the park without wheeling them back through guests, or admitting an ambulance into the park. Neither of these are a good idea, so it kinda makes sense to put first aid there. The rest of the building could still have stayed an arcade. Probably doesn't get the foot traffic that main street \ wb kids does though...