Yeah, and even those who did have armor thick enough to not worry about deflection worry about other things, like mobility. Plate armor as some may think of wasn't suppose to be heavy and hard to move in; this is a very bad idea if you're expecting people to fight in it. While you're not exactly going to be an acrobat, you can still be nimble if you're use to what you're wearing. People in the type of heavy armor that allows for little mobility tend to face issues like what happens when they fall, or get stuck in mud. Suddenly all that armor just makes you a sitting duck. Just long enough for some peasant with a spear to take a few pokes at your eye sockets.