If a casino decide not to compensate her users just because some random gamblers misused the privilege for customers to earn more bonuses then I would not blame the casino for such a decision because there has been high cheating on casinos that tend to be generous by greedy one time users that are only interested in getting the bonus and less when such opportunities to cheat are not available.
Casinos need to be stricts most time and bring those greedy gamblers to book. There are still casinos that don't do enough or reward their customers enough and that alone can learn to frequent lamentation by real users.
Casinos run marketing like bonus programs to bring benefit to their users and expect to receive good returns from funds spent for marketing. So it's reasonable that they are strongly against cheating in any bonus program that harms successful probability and level of their marketing. No company wants users to cheat them especially to steal money from the company without good return.
Users if breaking a casino's ToS or its bonus program terms must prepare for very bad consequences later if the company detects such cheating activities. They can try to make apology but surely the company won't accept it.
When a casino users cheat a casino, it limit the number of players that are allocated for such bonuses and it wouldn't make sense when few people are benefits due to multiple accounts.
There are so many players that are very good at jumping from one casino to the other, checking for the latest contests, bonus rewards so they can grab them with multiple accounts. Many keep doing this and getting rewards by casinos that don't have a strict policies or sophisticated detective tools to help fish out the bad and cheating players.