Tbf if he just built electrified trains everywhere in the world, he'd run out of money before finishing a single continent.

Think about it: He doesn't have a trillion dollars (or even a few hundred billions) in liquid cash. It's all in the perceived value of Tesla, which is about 30x overvalued (price/earnings being around 300, 10 is considered a normal healthy value). The more electrified trains everywhere, the fewer cars needed.