Lots of people have built commercial, non-military, boutique scale stuff in hardened facilities, nobody I'm aware of has done it at scale. There's certainly money to be made from selling expensive "we put datacenter stuff deep down inside a mine" maybe to some weird enterprise and government customers, so the revenue per rack (or per theoretical 208V 30A circuit?) is probably a lot more than commodity colo. But I would very much like to see the aerial photos, if anyone can link them, to a claimed large scale underground or hardened datacenter.

It's a severe engineering challenge to hide massive heat exchangers on the scale of the datacenters built in the industrial area near Dulles (coordinate example: 38.9817915,-77.417775). Find those on a map and observe the scale of their cooling and generator systems and then try to find anything comparable that's been built underground.