You need to understand this that gambling is a broad thing to discuss and we have numerous means through which one can make earnings from it, they are in categories and not necessarily you gambles by placing bet, you can provide them with your services, advertise for them, be their employee, or have something valuable to any gambling company which they deserve your service and pay you for, you can also own a small gambling point within your locality on a kiosk and you can as well bet which most are found doing and betting is also in categories, the higher the risk the higher the odds, all we are concerned at the end is that you earn a living through gambling and not rubbery.
I think you are referring to gambling in general but the gambling that we are talking about here is the one that you will play inside a casino or a betting shop. Here in online gambling, it is still possible to earn without placing a bet because there are gambling sites here which let you invest in their bankroll or in the house.
There's also casinos which has their own token. You can buy and stake their tokens to earn dividends. I think this is much safer if ever one decided to make gambling as a source of income. Overall it will be better to have a reliable source of income and only make gambling/investing as a side hustle to earn extra income.