I think more than climate it tends to be 1) what does the current construction look like and is it feasible to move lines underground, 2) what is the soil like, and is it stable enough to bury cables, and 3) are current property owners willing to accommodate the disturbance to trench and replace the old cables.

I grew up in an old (for the US), hilly east coast city and nothing was underground. Because it wasn't very dense and didn't have gridded neighborhoods, it would have been quite expensive to run utilities underground. I subsequently moved to a newer part of a different city and all the new construction had underground utilities. It still doesn't prevent outages at the substation or high voltage transfer line layers.

UK as well, we bury all (well technically damn near all) our sub-station to residence cabling and we are a wet country.

Power outages are a once ever few years or more thing.