Comment by Mountain_Skies

There are various degrees of clear. You might be surprised by how much scrub can grow there between clearances. Also the grade of the land can change quite abruptly. It's not like a railroad right of way where the grade is very limited. There can be significant ravines between pylons. The powerlines don't care because they're up above it all anyway. Pipelines likely have better paths but I suspect those are monitored more closely than power lines.