Honest question here: I'm from Italy and here we have problems with fires as well. However, here power lines and district transformers are placed underground except high voltage and ultra high voltage ones, but those are above tree height and rely on much sturdier metal structures.

My understanding is that burying power lines is cheaper in the long run and less prone to failures (trees falling, cars smashing the utility poles, ...). Therefore, why can't this be done in the US and especially California? Or is it already done for new developments? If no, is it because of regulations?