Why do some games not let you aim straight down? - Anatomy of a Player Controller

After the implementation of AI in the previous video, I needed to add hitboxes and health on the player character, and in the process of doing so ran into an interesting issue. I didn't see a ton of information about the non-code parts of setting up a player controller, so I did some research and tried to break down my findings in an easy to understand way. Hopefully someone finds this helpful! ... https://www.youtube.com/watch?v=Nq7QjRKr01k