Trenching (dirt/grass) and boring (road or driveway) are both much more expensive in comparison to just running it overhead with poles. You first have to add the surrounding conduit cost in to properly protect the cable from water damage compared to just hanging it up. Easements are about the same I believe between the two but I’m sure, depending on the place, those underground easements will have to deal with more obstacles such as existing water and waste rather than just throwing up a pole every 200’.
Then there is also the troubleshooting issue for line crews for if a cable faults out, you then have to dig out a much larger section to first find the issue then to splice it rather than just splicing the overhead line with a normal line crew and splice kit.
I can’t remember the exact numbers but I think the ratio for overhead, trenching, and boring was around $4/6/8 per foot making it over twice as expensive to bore over just throwing up some poles. Numbers can definitely vary, but most utilities probably won’t want to trench and bore unless they have to.