A lot of long-distance, high-voltage transmission crosses what's effectively wilderness. You've got issues of unstable slopes, earthquake faults, flooding, and ground-current losses (a big problem with undergrounded power).
And that's before you look at getting crews in place.
Then there's the question of monitoring, servicing, and repair after undergrounding.
It's definitely an option. But not a cheap or universally applicable one.
Not sure about that. The high risk places are also often in remote, rugged terrain. What you save by not having to disrupt other infrastructure you might end up spending just to get people and equipment to where they need to be. Interesting perspective here: https://www.wsj.com/graphics/california-wildfire-pge-drought...
Well then everyone has local solar with a powerwall for when PG&E shuts down. Maybe that's cheaper? Honestly I think PG&E could bury the lines cheaper than $750 a foot.
Maybe ultra sparse settlements on a scale as today are unaffordable in the long run? It not just power but also the roads and communication links. Accounting for infrastructure maintenance is not done properly.
Math: 155147 miles * $750/foot
And an article https://www.desertsun.com/story/news/environment/2019/10/11/... confirming it's pretty much out of reach. $15,000 per household estimate (and 1,000 years!!).