The few reasons I'm not flying in the US (I'm US Citizen and FAA licensed) is because of the following:
1) Job Security
2) Low Pay for regionals
3) There is more to the world than the US
The only airlines I would fly for is major airline Cargo, Fed Ex, UPS, Atlas, NWA Cargo, etc etc.. but since I'm in no hurry to fly a 747 (Even though I want to fly MD11s) I'm happy being an expat flying piston'd charters