Mesa does extensive international operations, and they do not want to have to schedule those ops around Captains who are not ICAO ATP's, hence every Mesa CA must meet ICAO mins.
ICAO mins are similar, BUT the big difference is that the US requires only 250 PIC, while ICAO requires 1200 PIC. You can get 50% credit towards most of this PIC from 121 SIC, but that can take a while...four+ years seems common
