I'm guessing you don't work in Logistics. Just a few problems:

* Airline operations and airport operations are relatively separate entities. What you're proposing requires buy in from all parties, while also forcing them to get into the ground transportation and hospitality business.

* Major cities generally have several forms of public transportation to/from airports. Buses, trains, etc. Creating an offsite center would require a city's mass transit agency to spend millions or billions to alter their transit routes -- in the case of trains, this also likely requires the taking of land through eminent domain proceedings in an effort to build new routes from city centers to offsite centers. Airports (airlines?) would then have to do the same to transport people from offsite centers to airports.

* Passengers might randomly disembark from their flights and get directed to offsite immigration and customs centers? Let's not even think about how their luggage gets sorted and sent to the right center, what happens if their car is parked at the airport or someone is waiting to pick them up or they have a tight connection from the same airport.

* You have a lot of instances where employees seem to be escorting people to places. (they will be asked to sit and an officer will approach you and guide you through the process. There won't be any lines and you can sit until you are called....their bags will be put onto the flight by porters...baggage agent grabs you a cart and walks you to your bag and through Customs.... a staffer would line you up by row. When your row is called you go through security. There would be lanes for Pre-Check, Families and Those who are frequent fliers but are not TSA Pre-Check and who know the drill so that way other TSA reps can be used to help infrequent travelers and families...For those with ticketing issues there would be offices for that where passengers would sit down and outsourced agents would help them). We all hate lines, but lines are efficient -- far more efficient than waiting for someone to escort/call/walk you from a waiting area to a desk where you're being helped.

Frankly, it sounds like a huge <redacted>.