Seattle’s main airport is surrounded by communities and has grown like a weed right along with the Seattle metropolitan area. It has no practical way to expand. Through recent technology and some clever evolution of facilities the airport authority is doing everything it can to shoehorn more passengers and flights into the same space. But there’s a limit. Airplanes, which are big and fast moving, need a certain minimum vertical and horizontal separation no matter how sophisticated the technology of the plane and control systems are. They also need to park and move around while they are on the ground.
The same is true of skiers and snowboarders at mountain resorts in case you hadn’t figured out where I was going with this.