Coupling falls off rapidly with distance. It's why a thick enough phone case will interfere with magnetic charging, and that's only on the scale of a few millimeters.

Drones consume a lot of power while in flight. You can get a little bit of power out of powerlines standing underneath them with some tricks, but it's not enough to keep a drone in flight. At least not without something prohibitively large to couple to the line.

It's also risky to hover near a stationary object because the longer you hover, the more you're exposed to the risk of a wind gust knocking you into the nearby obstacle.