It is significantly cheaper than burying lines from an initial cost point of view, so as long as the cost of preventive maintenance is low enough, it is a viable option. Particularly if the cost to fix lines is also low.

As an added bonus, it then also becomes easier to hang other lines (telephone, cable, fiber) on the same poles. This more difficult to do with buried lines, even if the lines are in conduit.

I’d prefer my electrical lines to be buried too, but I at least understand why they aren’t.