The dominant factor is "balance of system" aka soft costs, which are well over 50%.[0]

Orbit gets you the advantage of 1/5th the PV and no large daily smoothing battery, but also no on-site installation cost, no grid interconnect fees, no custom engineering drawings, no environmental permitting fees, no grid of concrete footers, no heavy steel frames to resist wind and snow loads. The "on-site installation" is just the panels unfolding, and during launch they're compact so the support structure can be relatively lightweight.

When you cost building the datacenter alone, it's cheaper on earth. When you cost building the solar + batteries + datacenter, it (can be) cheaper in space, if you build it right and have cheap orbital launch.

[0] https://en.wikipedia.org/wiki/Balance_of_system

Right now it is.

However, the amount of available land is fixed and the demand for its use is growing. Solar isn't the only buyer in this real estate market.