can someone answer me this question. If the companies themselves that manufacture the hardware systems why don't they just make then and mine for themselves? Rather than sell? Doesn't make any sense to me.
But they are already doing it, sometimes just stress-testing but sometimes looking to earn some extra coins until the next rise in difficulty, thus affecting the profitability of their customers' investments. AFAIK BFL, Avalon and KNC all used to do it.