Having 50% of of a watermelon is still bigger than a whole 100% of a grape fruit. I'm sure they've made enough that capital isnt an issue so why didnt they put their own capital (afterall you said warehouse and operating cost is cheap) and gain 100% revenue?
Yes it's for profit but the franchising won't enable them to buy extra hardware (in the short run at least). If the hardware doesn't go to franchisees it will end up in a giant datacenter.
My guess as to why they don't just build their own mine is that is would require tons of extra capital, time, effort and might be less profitable.