[schiffern]

  >why would putting them in Space, far less accessible in every conceivable way, with numerous additional expenses and engineering constraints, be cheaper?

Because mostly AI is power hungry, and in space you need 1/5th the solar panels, almost no solar panel support structure, and almost no daily load shifting batteries.

As it turns out, this matters more than launch costs or cooling radiators or radiation bit flips. This is why you need to do the math instead of assuming you know what the solution looks like.