Unlimited or Infinite Blackjack is when every player plays the same hand, and every player has the option to "hit" or "stand" at any time. Once you stand, the hand will continue for other plays who have hit, but not for you.
The outcome of a small number of players making huge bets is unpredictable. The casino could make record profits, or the players could wipe out the cash in the casino or eliminate the profit for the month. Maximum table limits prevent the casino from taking too much of a gamble.