Why are players allowed to make "smurf" accounts?

High elo players making "smurf" accounts should be banworthy. How is it fair that a challenger can make a new account and play in low elo? This completely ruins the experience of ranked solo que. It is not fair to the players winning or losing. Letting challenger summoners play in gold plat or diamond elo is like letting a major league baseball player play on a high-school team. It simply isn't fair. It enrages me to see master/challenger streamers on twitch do the Bronze to Challenger in 30 days challenge.