You would pay thousands for each meter of duct built including resurfacing whereas you would likely stand two poles with the same distance for less than a grand.

Take it that overhead is more likely to cause future issues, they would need to be significantly more for that to be the case. Where this comes in is regulations on SLAs and fines, loss of service costs. But on a pure cost basis it likely would take a long time for underground to balance out.

Companies also dont care and would prefer to lower build costs at the risk of future operational costs