Because they are extremely loud, consume 8-10 kW, and probably cost $20K used.
The 8-10kW isn’t a big deal anymore given the prevalence of electric vehicles and charging them at home. A decade ago very few homes have this kind of hookup. Now it’s reasonably common, and if not, electricians wouldn’t bat an eye on installing it.
Plenty of home runs all electric heating systems. Running inference on a H100 could be dual-purpose and also heat your home! (albeit less efficient than heat pumps, but identically as efficient as resistive heating)