I couldn't tell you for sure how I would design it differently. What I can say is that it is my understanding that most people have a loss-aversion tendency that overpowers their wanting-of-gains tendency (I'm not using the correct scientific term for sure haha).
For example, if you come up to people and tell them if you flip a coin, heads they get $10 and tails they gain nothing, everyone will take that bet. However, if you tell them heads they get $20, but tails they lose $10, a large portion of people will then not want to take that bet, even if the expected value is the same, because they value the $10 they already have more than the potential $20 they stand to gain.
Applied in your game, I reckon most players feel like the pain of crashing 2 planes is disproportionately worse more than the joy they feel when they pilot the air traffic expertly. If it's still the design you want to keep, I think there's a lot of feedback you need to design into the UI so that the players get rewards much more often, or disproportionately bigger than the crashes to counteract this emotion.