Most people will be baited into registering into a casino and playing their games because they saw an offer of great prizes and bonuses but once they are done playing they will realize how they weren't able to fully maximize the prize or bonus they were promised in the first place. Either way, the casino already got whatever they wanted which is to get more people to register and play. The question of whether they will keep playing is a different conversation but getting people to play at your casino is result of a successful promotion.
What will determine if the people that were convinced to gamble in the casino will continue gambling there or not is based on the experience they get while they visit the casino. Even if it's not entirely possible to meet up with all the promised rewards, there is something that can still keep some of the players with that casino, and the few among all the new players will be able to get out with great rewards, and they will continue to gamble there and can still indirectly refer others to come.