Electricity, support, lawyers, and (with cheap 1u intel servers and ec2) servers are costs which scale with demand. You don't have to spend money on those if you don't have money coming in the door. One airplane is really expensive. If you're an airline you're forced to make bets on future demand which you might lose, and the likelihood that you'll lose is higher when the market for your services is volatile (as in times of high growth).