Airports and customs are the face of a nation to most of the travelers that visit, the first point of contact and as such they leave a lasting impression. Think of them as ambassadors. If that first experience is a bad one that will reflect on what people think about the rest of the country.
Well, not quite. I also spent some time in LA on a different trip. It was a while ago (so not an adult perspective) but mostly I remember walking through carparks and hundreds of channels with nothing to watch. Seattle was a bit nicer as a place.
I would like to go back some time, just not right now.