The real reason is domiciles. XJT guys can go to CAL and not move. They have the same domiciles so it is a no brainer. Keep your house/schools ect and make more money at a major. Skywest is totally different. Senior captains in places like PSP/PDX/SAN/SMF/MRY or even FAT will never leave because they want to be based at home. Many others stay on just hoping to move into a captain slot in one of these domiciles. Many Skywest pilots have been hired at CAL and other majors but the total numbers will never be as high because the opportunity to live in a certain places and be based there is only available at Skywest.