Yes, casinos did change to multideck - but to attract players, many casinos offer game play with limited numbers of decks, and then ban extraordinarily rare players who can actually take advantage of the limited number of decks.
Gambling is all about trying to use the rules and the game play to your advantage, and that is what Ivey did. He played by rules that the casino agreed to, they are mad that they didn’t know the reasons for the rules they agreed to and want a do over.
