Space is a vacuum. i.e. The lack-of-a-thing that makes a thermos great at keeping your drink hot. A satellite is, if nothing else, a fantastic thermos. A data center in space would necessarily rely completely on cooling by radiation, unlike a terrestrial data center that can make use of convection and conduction. You can't just pipe heat out into the atmosphere or build a heat exchanger. You can't exchange heat with vacuum. You can only radiate heat into it.
Heat is going to limit the compute that can be done in a satellite data centre and radiative cooling solutions are going to massively increase weight. It makes far more sense to build data centers in the arctic.
Musk is up to something here. This could be another hyperloop (i.e. A distracting promise meant to sabotage competition). It could be a legal dodge. It could be a power grab. What it will not be is a useful source of computing power. Anyone who takes this venture seriously is probably going to be burned.
It's perfectly possible to put small data centres in city centres and pipe the heat around town, they take up very very little space and if you're consuming the heat, you don't need the noisy cooling towers (Ok maybe a little in summer).
Similarly if you stick your datacentre right next to a big nuclear power plant, nobody is even going to notice let alone care.
Heat pumps are magic. They're something like 300% efficient. Each watt generates 3 watts of useful heat.
Think of heat like flowing water or charge. Only an altitude or voltage delta creates the flow needed to harvest energy.
You get no useful energy from heat you are already trying to shed because you have no delta to work with. (The entire problem exists because there is no surrounding environment with high heat capacity and lower heat.)
Using higher heat to raise lower heat is just the most simple case.
But purpose isn't relevant to this constraint, it is a physics constraint. Regardless of purpose, you can't extract useful energy from heat without a heat difference to work with. (And without a heat difference, even "heating" with heat doesn't do anything.)
But I don't really see how that is relevant to the question of using waste energy to heat homes. We don't have ideal Carnot machines so there's always energy wasted, which most of the time is still good enough for residential heating.
The conversation was about harnessing energy, from heat, in orbit.
Heat pumps take energy to move energy. But you can't power the heat pump from the heat it is already pushing against the heat gradient.
Waste heat can be used, if there is a difference in heat to work across, but not if there isn't. A datacenter in Antarctica could recover energy from waste heat, against the freezing outdoor temperatures.
In orbital systems, the problem is getting rid of heat, so there isn't some cold place to use to create a heat gradient and harvest energy. Space is cold, but particles are so diffuse they have little heat energy capacity, so essentially a heat insulator, and not useful to create a gradient. Thus the use of radiators.