Deep Geothermal goes deeeeeepppp to where there is a heat source that is replenished.

Shallow geothermal pulls heat where there is no replenishment, and you have to run it in reverse (use it as an AC in the summer) to swap out the heat. You can’t only pull heat out for shallow geothermal. You may be able to for a time, but also remember that heating for a house is pretty small overall.

It’s not the entire earth that is the heat sink, it’s a relatively short distance from the pipe. We don’t get the massive heat from the molten core at the surface.