Because the people building it find value in doing so. Why does someone learn woodworking and make a chair when they can buy one from a store? Or why do they c

Because the people building it find value in doing so. Why does someone learn woodworking and make a chair when they can buy one from a store? Or why do they come up with their own design when they could follow someone else's plan? Creativity can be a lot of fun, particularly when not bounded by practical concerns.