Where I live on the coast, fires are easily contained. Just 20 miles inland it's a tender box that can burst into flame with just one spark.
As wild-land fires goes transmission lines are seldom a problem, as the right of ways are cleared so wide there's hardly a tree that can knock the lines down.
The 12 KV distribution, on the other hand, covers a much broader network through the mountains. Those right of ways are cut more narrow through mostly forests habitat. No surprise trees are a major cause of fires. But percentage wise, regionally, human activities rank as the major cause of most wild-land fires.
It would be expensive to put all distribution lines underground. Sounds good, though.