Trump thinks of himself as a powerful, insightful deal-maker. He pathologically needs to feel like he is doing something and his comfort zone for what kinds of things to do is "stuff that feels like business deals".

He knows very little about government and policy, but tariffs and dollars and percentages feels familiar to him. He's got a lever, and he can't resist yanking on it to show that he's in charge.

Whether yanking on the lever actually benefits the country or him is entirely besides the point. He's a narcissist and narcissists can't let go.