He doesn’t understand the nuances of making policy decisions, so his default answer to stuff like this is to just impose tariffs because that’s all he knows. He doesn’t care to understand and would likely eat the crayons you use if you were to try to explain it to him. He’s just incapable of that sort of mental growth.
You’re giving him way too much credit. Never attribute to malice what can be explained by stupidity. While Trump has certainly performed acts out of malice, he is also the epitome of stupidity. He’s suggested nuking hurricanes, injecting bleach, and has stared straight into the sun during a solar eclipse, etc, etc. He’s a terrible person of course, but he’s also a complete moron.