I’ve done a couple of deep dives in a flooded silo for my Master Diver certification class. It was a very cool experience with crystal clear water as long as no one disturbed the sediment.
It's a small underground facility in the middle of nowhere in Kansas -- even assuming that you could get adequate power service and bandwidth to the property (which is unlikely), you're still trying to run a bunch of servers out of a tiny, damp, hot hole in the ground. Not ideal.
Every time I see people proposing to turn a former missile silo into a datacenter, I'd like to ask them to first do the budget on running a geographically diverse ring of singlemode fiber to the nearest mid size city...
Most of them are located in areas with little to no real telecommunications infrastructure.