Contrary to the popular belief , casinos don't have huge profit margin. From my experience , they have less than 10%, after they pay all the taxes and licenses, and taxes for these kind of business are quite high. Truth to be told,i worked in Europe where taxes on these things are quite high, some specific places like Vegas or Macau might have lower taxes.
So it is not so easy, to just open casino and make easy money.
If you look at a real casino, then the payout percentage is up to 98%. And the casino lives on these 2% very well) The main thing here is to have a big turnaround. In an online casino, it is not known what percentage is paid. And this is the main problem.