because you still need a cable with a lightning end in your spaghetti of cables in a drawer somewhere. if all of your devices had USBC on both ends, then you don't need the one cable with the special adapter. you just need USBC cables. this isn't rocket science, and it's not a hard position to be sympathetic with either.
Having everything be usbc makes sense.
Having everything be lightning makes sense too, but is infeasible. Lightning was never going to be good for almost all devices, like usb mini-b, micro-b, and now usb-c have managed to get to.