One, category 6A cables actually cost two and a half times as much as a basic single mode fiber patch cables. Two, cable diameter. Ordinary LC to LC fiber cables with 2 millimeter diameter duplex fiber are much easier to manage then category 6A. Three, choice of network equipment. There is a great deal more equipment that will take ordinary sfp+ 10 gig transceivers, then equipment that has 10 gigabit copper ports. As a medium-sized ISP, I rarely if ever see Copper 10 gigabit.