[teddyg1]

When flying, spotting anything from a higher elevation is very difficult - you essentially have to track the differential velocity of the bird / plane with respect to the ground. That's the reason why generally, the right of way in air goes to the airplane with higher elevation.

Adding additional things to spot in the air, especially slow moving objects like drones, demands focus and divert attention away from flying. Other airplanes in the air are fine to spot because they move quickly, and in unrestricted airspace, generally communicate on a universal radio channel. Drones have none of these capabilities and are essentially high flying birds to avoid.

In non-urban spaces, airspace above 500ft is always a potential manned aircraft flight path.