There's no air and negligible thermal medium to convect heat away. The only way heat leaves is through convection from the extremely sparse atmosphere in low Earth orbit (less than a single atom per cubic millimeter) and through thermal radiation. Both of which are much, much slower than convection with water or air.

Space stations need enormous radiator panels to dissipate the heat from the onboard computers and the body heat of a few humans. Cooling an entire data center would require utterly colossal radiator panels.