Because these pilots wer TOLD that they were going to be let go! Instead of waiting until the day they got let go and then being with out a job they decided to be proactive and find a new job and then gave Mesaba notice that as they were going to be laid off ANYWAYS they would be leaving.
A first year pilot can not go months without a paycheck. He or she can't just wait to be laid off and then go try to find a new job. Getting on with an airline can be a long process thus they got the ball rolling before they were screwed and left without a paycheck.
Additionaly these guys only make about $20k per year at the beginning and on top of that have $40,000+ loans from training to pay off.
This is a reprehensible move by the airline!
Additionally, the temporary furloughed argument is ridiculous for two reasons.
First, they would not have been back on before the one year contract was up.
secondly, a Pilot at that stage in his career CANNOT go for an undetermined amount of time without a paycheck.