Burying power lines is non-trivial, there are parasitic energy losses from the change in capacitance when the wire is placed closer to the earth. I believe this is not an issue in "distribution" lines, but for "transmission" lines it would require changing to a HVDC system which requires expensive equipment and limits distance. From what I have read it was "transmission" lines blamed for these fires.
There are numerous other factors to consider too; for example I believe above ground lines have been proven to be more resilient in seismically active areas, etc...