system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why weren't light gun controllers like GunCon being used in console first person shooters like Halo?
gpt
Because if you're using a light gun, you're not using a controller, and therefore you generally don't have any way to move your character. Almost every light gun game was on rails. 

Some light guns had a D-pad, but it's pretty jarring to try to pull the trigger while simultaneously holding down a directional key to move, and it wouldn't be as dynamic because you'd have to play finger Twister to jump, shoot, and move in a direction at the same time.