Some radioactive decay still is believed to go on there, e.g. thorium. That keeps the core, that is mostly iron, liquid. Weird. We’re sitting on a dirt-and-water crust on a big molten radioactive iron ball. And it doesn’t just sizzle off.
Now you are speculating. You don’t know that we have an iron core - it might be uranium.
I had just never thought of it as a reactor, God’s reactor covered with enough shielding that humans can thrive. Oh, what a fortunate accident.