But why why would you do that?

because he wants to

Well, this could mean several things.
He could be running because he wants to get somewhere quickly. Perhaps he's late, or excited to get to his destination.
Or maybe he's scared and is running from something that could catch him.
Perhaps he's just been rejected and is running away because he's embarrassed and needs to put distance between him and his crush.
(Or idk just take it literally like a boring person, I am an English nerd)

Well yes.