According to this document [1]:
"The North Carolina Utilities Commission studied the cost of placing Duke Power’s distribution facilities underground and found it would cost more than $41 billion, resulting in a 125 percent increase in customer rates."
[1] http://www.sceg.com/NR/rdonlyres/465E6534-2FFB-4069-BF84-814...,
I've also never heard stories about issues with rats.
Power outages still happen, but they are quite rare - in 30 years I can only remember twoish.
Apparently it's the insulation on the wires that they like.
Like it's gonna be some unprotected plastic cables 1 foot under the ground?