Or you could wash the wings once in a while. You're on the tarmac for over an hour while:
- Passengers are busy boarding despite their boarding group not being called.
- Crews are not loading your luggage.
- The pilot is working on his second cup of "sober up" coffee.
- The flight attendants are gossiping about who fucked whom.
Might as well have a guy spend 2 minutes hosing off the wings. Impact of build-up during a single flight surely falls below the point where applying and maintaining a fancy coating is cheaper than having Jose hos-e off the bugs.
Bug guts are sticky. They do not simply hose off. You need to actually scrub them off, and if you're doing that, you need skilled labor because there are lots of sensitive things that stick out of aircraft.
More than one aircraft has been lost because someone missed removing some tape covering some hole or other that was applied in order to wash the aircraft.
And there's a lot of surface to scrub, too.
Even little bug smashers like Cessnas take a good while to clean off (and flying through a bog meant you often flew through a crowd of mosquitos, so the leading edge was covered in lots of little red spots).