I imagine it might come down to how much money the airline is willing to put into the necessary infrastructure. Paranoid security changes after 2001 might also have shut that sort of thing down.
Yeah, maybe an airline can say to the airport/CBP "we'll pay to rent a lounge/corridor/gates at this airport in this terminal for a sterile transit option between our flights or our partners' flights because some passengers want that" and maybe the airport/CBP can approve the proposal. (Maybe non-U.S. passport holders will still require an ESTA, but not a CBP examination?)
I think the specific option at LAX was post-2001, but you had to be on a specific pair of flights to take advantage of it. (I didn't do it, I just read about it on FlyerTalk and forgot the details.)
I think the specific option at LAX was post-2001, but you had to be on a specific pair of flights to take advantage of it. (I didn't do it, I just read about it on FlyerTalk and forgot the details.)