I see this a lot in Miami when AA passengers discover that the Caribbean and most of Mexico plus Canada is not international travel when they are in J and thus get no access to the Admirals Club. Also at the new Club those who get in via club membership then try to get into the new Flagship Lounge (shared lobby) with the same proviso that it's only for international J and F and not the Admirals Club which I presume must be jammed with domestic passengers.
So not chancers but people used to airlines where all J/F is a freebie lounge invite.