Maybe I missed it but I don’t think they are talking about putting high tension underground. Around here, the power companies take pretty good care of the tower lines as far as tree incursion and maintenance of way goes.
The overhead residential lines are the ones neglected when it comes to trees. I still say $15 mil a mile is BS for putting medium voltage (~13kv.) underground.
Just looking at what’s running above ground in my neighborhood, it would be a freaking nightmare to do it