Changing a light bulb on a small airplane may be easy, but changing a tail light bulb on a 747 may require shutting down the APU, as well as finding a cherrypicker or other lift to get there in the first place.
Nav lights fail often enough that many airplanes have 2 separate bulbs in each position for redundancy. I believe LEDs, if they meet the visibility and color requirements, would be ideal for this application.