Bonuses are an essential part of casinos as marketing strategy to encourage customers on using the casino and attracting new users too. There is no explicable excuse to make it look as though it's the fault of casinos make bonuses available in their platform for their customers. Anyone caught abusing the bonuses terms deserves any consequence allotted.
That's true. Customers deserve high bonuses and contests. Because of greedy gamblers who want all of this for themselves, the casino won't stop providing these offers.
The only thing the casino can do because of greedy gamblers is to regulate them and be strict with those who are caught. Bonuses and contests are a way of promoting a casino to gain more customers, so they are part of the business that the casino can't put a stop to.
If by virtue of greedy gamblers that abuse the bonuses system and a casino then decides to halt bonus offering to its customers that are due it. Such casino would only be making a bad business for themselves because it's going to drive customers away from the casino when they realise they are not getting bonuses anymore as it were even with how much they spend gambling.
Of course, a strict regulation can be helpful.