Is this true though? PG&E has to seek approval on rate increases. From all reports it is expensive to bury power lines, and PG&E would need to raise a significant amount of money to bury even a small percentage of their lines.

(Fwiw this is just a gut feeling, I don't have actual numbers to back anything up)

It is theoretically possible to bury every transmission line through remote country brush, only as long as there’s anyone left in CA willing to pay to draw electricity from the grid by the time they’re done doing it.

Remember state-wide we’re talking about ~$5b of energy (generation cost) per year. How much do you want to pay to transmit that $5b of energy?