Thin profit margins, sure. But....the above examples of the E145 vs an ATR. 40% more fuel burn on a 400sm leg with the jet, no appreciable time savings with an ATR on a 300 NM leg. ATR costs less to buy, and carries 18 more passengers. It would work unrestricted. on any route east of Colorado or along the west coast. Do 8 legs a day 7 days a week 52 weeks a year and there's a huge profit margin - factor in a fleet of say 50 and the profits are "more huge", tens of millions of dollars. However, I am sure mainline essentially says what aircraft to buy (presumably so they can also operate on 200 and 1000+ nm segments) and also knows the costs of their operation. Then makes sure their contract isn't going to give anything but thin profit margins to the contractor.