>>63988738As the first guy said, undercutting was what basically won the contract; however, another consideration is that while all the companies built a "modular" pistol that met the army's specs (can put a red dot, rail for light and laser, and interchangeable grips for manlets and women with tiny hands), SIG marketed the FCU as solving a problem that armorers had. If an important part breaks, rather than replacing the whole gun, it's easier than ever to just replace that part.
No longer do you need to worry about the crayon eaters breaking the frame by using it as a hammer to break down rocks, because if they do, you can just get a new frame.