Why do we use behaviour trees and AI controllers

Im currently working on some enemies for an idea i have. Im new to unreal so Ive been following some tutorials from epic and on youtube from others.

I’m trying to figure out why you would use a behaviour tree and an ai controller instead of just putting the instructions straight in the actor blueprint. Is it just that behaviour trees are easier to set up the flow and conditions of actions or is there another reason?

Sometimes i find myself putting instructions in the actor blueprint and then questioning if they would be better off in behaviour tree tasks. But then again, im not sure there is even any real difference if they both have the same outcome.