They also could have built the garage at the back of the parking lot because putting it right in front of HR would have blocked access to HR and Gate 3(?) during the construction. There’s also, probably, fewer underground infrastructure further away from the park that would have to get rerouted during construction. Plus, most of the surface spots that would be unavailable during construction of a close garage are... let’s see... handicapped and management parking.
HHN cast has to park in CityWalk because employee parking is so limited. This decision has nothing to do with expansion.