Good point. Is it also true that high risk places (forest/rural) are probably cheaper and easier to install underground than low risk places (urban)?

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...