"You'll be claiming that they don't ban big winners next"
Casinos ban people who win big - and regularly - at games played against the house because the odds in such games are loaded in favour of the house. Anyone who wins them regularly is probably shaving the odds somehow, the most common method being card counting in blackjack.
However, casinos never ban people who win big at poker because it's not their money being won, and because having a famous poker player at your tables attracts gamblers through the door. Moreover, casinos make their money from poker through the rake, which is basically a small percentage tax on each hand. The bigger the hands, the bigger the rake - so keeping those big winners who play high stakes poker at the table is more profitable.