When you introduce an element of "chance" in winning cash, it's basically a sweepstakes or lottery and has to be properly registered as such. Since the process is slightly different and separate in each of 50 states, it's not feasible to do -- too expensive, too difficult, and all for a feature that would most likely just cost us money to operate. This kind of suggestion comes up a lot, and unfortunately, this is why we haven't been able to accommodate it.