There are very high temperature transistors.

We don't use them on earth because we expect humans to be near computers and keeping anything extremely hot is a waste of energy.

But an autonomous space data center has no reason to be kept even remotely human habitable.

The transistors are experimental, and no one is building high-performance chips out of them.

You can't just scale current silicon nodes to some other substrate.

Even if you could, there's a huge difference between managing the temperature of a single transistor, managing temps on a wafer, and managing temps in a block of servers running close to the melting point of copper.