"Common sense" does not always equate to facts or relevance. While, yes, the cost to dig up a line is likely to be higher than the cost to repair a hanging lin

"Common sense" does not always equate to facts or relevance. While, yes, the cost to dig up a line is likely to be higher than the cost to repair a hanging line, that's just one cost and consideration. Economic loss due to wildfire as well as rolling brownouts to try and avoid wildfire are both costs you'd need to consider. You also have the cost to maintain vegetation around powerlines, vs basically no pre-emptive maintenance on buried lines (and little to no weathering). And you, of course, have differing likelihoods of the line breaking in any case, which means the per-fix cost is only part of that picture. Lots of potential reasons, but I'd be curious to see a full study on those reasons for both above ground and below ground, their potential solutions, and their potential costs, but without that you have a very fuzzy picture.