I do not know why your cable box is turning off of its own free will. However, my virtual remote (using Slingplayer for PC) has a power button and I can turn the cable box on or off remotely. In fact, I make a point of turning it off when I am not viewing. I suggest you check your virtual remote to see if it has a power button: if it does, then you do not need to ask someone at home to power the cable box on for you.
You could also swap cable boxes to see if the problem persists with a different cable box.