But that's backwards: the point is, any player who possesses only 500 YEPs and enters a 500 YEP mini is engaged in a match that is certainly reckless and possibly suspect. Since the TDs can't police them, as you reiterated (they can be tossed in plain view of the TD), it makes more sense to regulate by entry qualifications.
As to sanctioning those who violate rules, we can and do impose sanctions on violators, happens all the time. It's just that this particular problem is not so easily adressed: where's the evidence? We're not trying to have a police state here anyway, just to set up rules that as much as possible enforce themselves, and YEPs limits on minis is entirely automatic.