> The obvious answer to everyone's concerns is to build them in unused buildings in cities that already have infrastructure to support them.

This is the problem.

These are mostly old office buildings.

They are not designed to supply that much electricity and water on each floor. These racks and equipment also weigh a lot and the building floors and building itself probably isn't rated for that.

Not only that, but to get the buildings themselves more electricity and water often requires a very expensive process of digging up possibly multiple streets, with associated costs and permitting.

In addition to the water delivery issue, there's power delivery. It may not even be possible to get that building enough power in the next decade or more, because there simply may not be enough power generation capability.

Basically, a lot of the same problems that exist when trying to turn an old office building into high rise apartments, but magnified many times over.