because if gambling activities such as betting or playing casino games are turned into a job, it is very difficult to make a profit or target a profit that can be used for living expenses.
If it were possible, many people would have already quit their currently jobs, especially the low paying ones, to live from online bets, without any effort while making huge profit in a very short timeframe. There wouldn't exist poverty anymore in the world, because as soon as someone needed money, they could access an online casino and raise some easy and instant funds. On the other hand, how could casinos profit and keep the industry alive and its workers paid then? Of course this money has to come from somewhere, and that is the reason why gambling can't be a full time job for gamblers, because if it were, it wouldn't be a full time job for casinos' operators and everyone else who work for the industry.