Moving less weight with the narrow stance squat is usually due to the increased range of motion, or because you're not used to it. The longer range of motion means that you are doing more mechanical work. You have to move further down and up. This increases the demand on your muscles, mechanics, joints, and time under tension. Others, they're just not used to the movement. I can actually squat more with the narrow stance version. But I have very narrow hips and long femurs, so the narrow stance is much more comfortable for me and I use it more often than other stances.