Space gets you 24/7 solar power. To run a data center for 12 hours without sunlight, you'd need massive batteries. Also oceans have weather and corrosion.

The issue with putting stuff in space isn't the kinetic energy required. In LEO that's about 30 megajoules per kilogram or $5 worth of propellant. The issue is that orbital launch vehicles are not reusable, so you must destroy an expensive rocket to get your payload to orbit. All of these space datacenter efforts are betting that Starship will be fully reusable.