You might as well question the realism of the rules of chess.
The rules of a game dont have to make sense and dont have to be realistic.
They only have to work as a game.
D&D5 is optimized to be easy to handle with nothing but pieces of paper, a pen, and a couple dices.
Thus things are kept simple. Not realistic.
show me how you dodge sword in plate armor :F or hit from crossbow xD
