The only main way that casinos generate revenue is through the losses of the gamblers, the casino owner only needs the start-up capital to build the infrastructure within the platform and also groom the casino until it is financially stable enough to run its cost on the revenue generated within it, but the main financial fuel for gambling businesses is the gambler money used to stake game and losing.
To be ahead in this, that is the reason that casinos implement the house edge system so that casino operators will have a bit of an edge to keep the revenue flow steady so that they won't run out of business.
Thats not true, casinos at least physical casinos have other ways that they generate money through hotels and other avenues through restaruants and other services that they provide. Even online casinos probably have other ways that they generate money apart from just the gambling like ad revenue etc. But hey you're right that the majority of their money is generated from gambling.