At the voltages involved in power transmission the "grounding" will cause an arc that'll do a lot of damage and take the transmission line out of service until

At the voltages involved in power transmission the "grounding" will cause an arc that'll do a lot of damage and take the transmission line out of service until it's dug up and fixed. And that takes awhile and costs a lot of money not to mention lost revenue while the transmission line is out of service. Above ground is the way to go since it's cheaper to construct and much easier to service when things go wrong.