Let’s imagine a world where time machines are invented.
Hypothetically, what’s stopping anyone from travelling to the past, where the dollar is much more valuable, and buying things at a much lower price? What if you then go back to the present, sell those things at a higher price and repeat the cycle? And wtf would happen if everyone there started doing that?
Does everyone know that time travel exists? Or is it like a secret? If there was only one, whoever controlled it either way would be all powerful and immediate ruler of all people on Earth. There’s literally nothing you wouldn’t be able to do, and no force could stop you. Economics would be yours to control.
If everyone had access to time machines, it would be chaos. Markets literally would grind to a halt, because time travelers would be perpetually competing to be 1 second ahead of their competitors, all the way back to the beginning of time. Humanity would inevitably destroy itself.