What if that particular load in your caliber is sold out? What if you want to zero your gun... now you're forced to have a dedicated gun for the game or keep your gun zeroed to this particular load regardless of what else you might normally shoot. What if you want to function test your gun but don't want to pay for factory ammo? What if you want to practice with your "match" ammo? Heck, what if for some odd reason that particular load isn't reliable in your gun but lots of other ammo, including your carry ammo, is just fine?
There's a reason so many competitive shooters reload, and it's not just to get the wimpiest allowable load.
I have seen exactly that -- right down to it being Speer brass -- before in a match that required folks to shoot their duty ammo. Give a valuable enough prize of even just serious recognition for the winner and someone will push limits. That is why you have power floors in the first place. Otherwise you could just say, "everyone shoot standard ammo, ok?"If people are so intent on cheating on a 50 round match that they reload Speer brass to recoil less and be easier to shoot, well then...wow.