1. every gram you need to send to space is costly, a issue you don't have at ground level
2. cooling is a catastrophe, sure space is cold, but also a vacuum, so the cooling rate is roughly the infrared radiation rate. This means if you are not careful with the surface of a satellite it can end up being very slowly cooked by sunlight alone not including running any higher heat producing component (as it absorbs more heat from sunlight then it emits, there is a reason satellites are mostly white, silver or reflective gold in color). Sure better surface materials fix that, but not to a point where you would want to run any heavy compute on it.
3. zero repair-ability, most long running satellites have a lot of redundancy. Also at least if you are bulk buying Nvidea GPGPUs on single digit Million Euro basis it's not rare that 30% have some level of defect. Not necessary "fully broken" but "performs less good then it should/compared to other units" kind of broken.
4. radiation/solar wind protections are a huge problem. Heck even if you run things on earth it's a problem as long as your operations scale is large enough. In space things are magnitudes worse.
5. every rocket lunch causes atmospheric damage, so does every satellite evaporating on re-entry. That wasn't that relevant in the past, but might become a problem just for keeping stuff like Starlink running. We don't need to make it worse by putting datacenters into space.
6. Kessler Syndrom is real and could seriously hurt humanity as a whole, no reason to make it much more likely by putting things into space which don't need to go there.
Last but not least, wtf would you even want to do it?
There is zero benefit, non nada.
Even this isn't true. It's ~120 degC in daylight in LEO. It only gets cold in the shade, but a solar powered data center is pretty useless in the shade.
That is converted to 2.5kW electic and 10.5kW heat. The electric is then used to power the computer and ply doom or whatever. That 2.5kW of electric is then converted to 2.5kW of heat. That means the satelite has to dissipate 13kW of heat.
But even without the electric use it still receives 13kW of heat and dissipates 13kW of heat.
Any object in space will emit as much energy via radiation as it receives otherwise it will continue to increase in temperature. The question is thus what temperature does it sit at to make this in equilibrium.
If the satelite was perfectly flat it would run at 120c for a black body. If it was a lump of stew it would be about 150c.
To reduce that to 20C you need about 50sqm radistor, or 5 times the surface area in shadow. The shadow is about 350-400m long
So you build it as a cone with the flat circular area facing the sun and the pointy area in its shadow you’d only need a cone height of about 20m to emit enough heat to keep the satelite to room temperature.