I am just honestly confused. There seem to be no logical reason for it, except that it would raise the stock value of rocket producers like SpaceX and Blue Origin.
necessary ground-based necessities for space based data centers?
They could be configured such that no off switch exists, no manual administration is required, and it's a fully self-sovereign system that can only be shut down by sending a missile to space, and physically accessing it to extract the data or encryption keys it contains is even harder.
you can easily fortify and militarize your data center on earth to the extent that no protester will ever come close?
Only if your definition of "protester" excludes anyone using weaponized drones, but that misses the point. The current meta for fortifications right now clearly favors the attackers, and that's especially going to be true for a facility requiring large power inputs. That meta no longer applies if your data castle is in space.