Without even going into the numbers, terrestrial data centers have significant cost advantages. They don't have to spend $$$$$$$ to get to orbit. They can upgrade and/or fix components easily (likely safe to assume a hypothetical orbital DC would plan to never replace anything). They don't have to pay for the full capex of their power generation facilities. Lower-latency Internet. Heat dissipation is a (possibly unsolved?) problem. For every input cost to a data center, moving it to orbit massively increases that cost.
From a pure engineering standpoint: orbital data centers are not optimized to solve any common problem faced by data center operators or users. Permitting can get difficult in parts of the US, but at least permitting is a solved problem.