#1 Supply and demand.
#2. Working conditions, work rules in Asia.. more than likely suck compared to the U.S. You have to pay more for people to put up with and stick around for stuff like that.
#3 Pilots here are willing to work for less in order to gain experience for the better jobs. -- And this is probably the main reason.
It's pretty easy for regional pilots to make 50K a year. 100k for a captain is easy also. Stick around for a while and the pay goes to 120-150K.