heating.
Radiogenic heating is key to forming a magnetic dynamo and plate tectonics. But, too much radiogenic heating and a planet can’t permanently sustain a dynamo, as Earth has done. This is because the thorium and uranium end up in the mantle, and too much heat in the mantle acts as an insulator, preventing the molten core from losing heat fast enough to generate the convective forces needed to produce a magnetic field.
https://phys.org/news/2020-11-radioactive-elements-crucial-habitability-rocky.html