Gambling sites is definitely a business and every owners invest their own money to make it grow and for sure they wont give free money to anyone same as you said they are not charity.lol. They would surely make an advantage to its players that why almost of gamblers of a gambling site actually losses on the long run.
Gambling sites is really a business and the owner of it for sure it can really make their way just everybody should gamble to their sites. And it is your choice if you wanted to gamble or not. So always be careful in every decisions that you will make.