Not all lines are on nice level land. Transmission lines go through some rugged terrain. I've seen some distribution lines that are in pretty rugged areas as well. They also mentioned the top down view was advantageous compared to a ground pounder's view, so a crawler would loose that view as well.

Delivery drones are leaving line of sight and yet they are operating. The Walmart near me started delivery late last year, and they are buzzing my area many times a day. I'd hope with enough testing these guys can work with the FAA to get certified to remove this limit.