There's a huge difference in potential blowback between mistreating some poor bastard from Pakistan who signed on as unskilled labor and a trained airline pilot from a Western country.

Edit: And how in God's name are you going to extort the passport from someone whose literal job is to fly an airplane to other countries, where they not only need it to do their job, but can just land somewhere and be like "peace out, I quit, I'm not flying this thing back."