Airports do have to be very carefully designed as you say. They are a complex set of interconnected facilities. But the upshot of this are dozens of different

Airports do have to be very carefully designed as you say. They are a complex set of interconnected facilities. But the upshot of this are dozens of different specialist teams who have conflicting interests. Communication is difficult and it is hard to maintain consistent state. In an operational airport this complexity still exists and major airports are in a constant state of flux. They are always building something and there are always contractors on site doing construction or maintenance. The difference is that it can be treated as an incremental improvement. No one can pretend that the entire system will be optimal first time. Of course the requirements will evolve.