Because the getting AIDS isn't worth a 20k bonus. Every responsible person knows to go to an airline with the shortest 1 leg commute to the fastest line schedule.
If your family can deal with you being gone 20+ days a month, they can deal with you being gone the other 10, and you are totally not needed or serve a purpose to them.
Guys in the past didn't have much of an option, so they did the best they could. Nowadays it would be purposefully inflicting tortue on them and yourself.