Surface level answer: because electromagnetism. It happens that for 2 currents flowing in one direction it’s energy-wise more stable to be closer to each other

Surface level answer: because electromagnetism. It happens that for 2 currents flowing in one direction it’s energy-wise more stable to be closer to each other - and wise versa. Deep level answer: nobody knows why exactly is that. Because electromagnetism is just a model to describe what we see with some math approximation. Maybe it’s just we were lucky to be born in the universe with such properties and able to talk about it. https://en.wikipedia.org/wiki/Fundamental_interaction https://en.wikipedia.org/wiki/Fundamental_interaction