Grab a club with one hand thumb up and the other hand thumb down. Notice how this limits your motion.. Grab the same club with both thumbs down. Notice how this limits your motion. Grab the same club with both thumbs up. Notice how you can swing freely, generating power.
Im going to point out a cultrual element here, you draw how to do something from past experiences. In the same way someone who has only done longsword would treat a staff like a longsword, if you did baseball (or any bat sport) you would porbbly insert how you held it and swung it in the situation as its the only informstion you have. Or if you have only seen it done like that.