Convenience. If you have a security camera up 50 ft on a tower 40 miles away connected to the internet via cell modem where do you put the PC? And is the PC able to fit in the power envelope and put up with environmental factors? An sbc is much easier to harden environmentally
I'd assume because of cost. This device does exactly what's required with low power draw and is easily replaced if it breaks or more processing power is required.
