I have not done gambling business before now and cannot say exactly how it feels or look like running one but making a response from asumptious point of view I would say it a profitable business because if it's not, many persons wouldn't be venturing into it and we wouldn't be seeing the growing number of online casinos all around, they are making money off it and that's exactly why people with the required capital still choose to venture into it not minding the large numbers around already.
As for how they make their profits and things that are needed to get started, I really don't know but for sure making money of it is realizable and owners of the casinos can be sure to be in profit even if they payout often, especially when they have got huge bonuses to drag in customers.
At least you are honest, even though I have no experience managing a casino business. Although I know that it is not easy to build a casino business. Because big capital is big risk but big income if managed correctly and properly.
I haven't seen anything cheap in investing in a casino; it seems like it's better to promote a casino online than to own a casino yourself. That's why you have to have a lot of followers to get a big advertisement payment.