well someone can pick the same map twice,not on purpose.
for example I got the MAblak pack,and mostly play Mablak maps.
I choose Mablak #10 in a game @ the start of a season,then i can accidently choose it again in a game @ the finish of that season.
let's say i would win a game vs a player with a hight TRL overall and i would play that game on a map that's picked for the 2nd time.(not on purpose)
that game would get void...imo that's not pretty fair