That's right, but still each electrically powered UAV trip seems to be better to air quality and CO_2 emissions than a trip by a combustion-engine-powered car.
people want to do them
Not necessarily. I think many people, including me, are perfectly happy spending whole day at home. It is very convenient when you can order something almost to your door, and it would be ideal without burning fossil fuels or exploiting delivery people.
Yep, this is sadly a physical problem in the essence, not created virtually by capitalist economy. The negative price is just how the capitalist economy reacts at it.