gas is cheap so you can't craft yourself into being stuck somewhere.
Example. You fly to a mission that isn't on a planet but on a ship in space (no mailbox) you complete mission, craft away while still at this location. you craft so much you only have a few credits left. No mail box on your ship, can't fly to a planet, can't fly to a space mission (to get credits etc) so that is why it is cheap so someone doesn't get stuck in space....
Though would be funny if it happened and you didn't have a fleet pass.....
Now they could raise the gas prices if they put a mailbox on your ship so you could mail some credits to your character if they got stuck.... but keeping gas cheap prevents people from freaking out about being stuck and getting a ton of OMG I'm stuck in space posts / cs tickets opened.