That's because airTran didn't like running RJ's.
You lost the airTran contract because of cost... to them. Pilot are only a small percentage of the CASM, but flying RJ's is a losing proposition unless you're connecting them into a hub with yields that support the loss.
airTran made somewhere in the neighborhood of .02 cents per mile in yield for passenger revenue last year; that came directly from the Chief and I'm sure was in the SEC filings as well. When the RJ contract is costing you .03 or .04 cents more than your revenue,,, well, you do the math.
The d*mn things are just money losers if you're not connecting pax onto an aircraft where you're going to make $200 per pax in yield ($1,500 to $2,000 round-trip flights to Europe or Asia). It has nothing to do with pilot pay or flight attendant pay or even mechanic pay; combined they represent about 10-12% of the operating cost of the aircraft. It's all about engine reserves, scheduled maintenance, rotables, fuel, and available seats (or lack thereof in a 50-seater).