Restriction is a widely used technique in both art, and life. Consider black and white paintings, or generally paintings which only use shades of a single color? Why are they not using all the colors when they exist?

What about people who do challenging athletic endeavors with limitations? The ice guy climbed up to the base camp of Everest in just his shorts and slippers. Why not wear more?

What about minimalism as a way of life? Why not buy more if you have money?

This is just how humans are.