There are rules that state that if a dealer has a blackjack, he wins immediately. The player is not allowed to draw. You should simply accept it as the established rule. And vice versa, the dealer is not allowed to draw if a player has a natural blackjack.
In order to avoid disappointment, learn the rules of the casino and find out what their house edge is before starting to play. There are options that are not available at every casino, but they can be beneficial for a player. The house edge will show whether the prize is high enough compared with other casinos.