A simple Google search shows underground lines are not only extremely expensive (most sources indicate 5 times the cost of overhead lines) but they are vulnerable to damage from flooding in low lying coastal areas. That means hurricanes will knock out power on the coast no matter where lines are located, but putting them underground will increase the cost and delay of getting to them to make repairs.

Reports are that power lines are blamed for the catastrophic California fires. It may be determined that the cost of moving them underground will be worthwhile in that area, particularly given so many neighborhoods were so totally destroyed.

The wisdom of moving lines underground is very much location dependent.