The reason why you need a jobs or business or both is because the winning you get from gambling is not consistent, it is not specific, it is not certain, it is not fixed. But your salary is fix and consistent and can also be increased based on your performance at your work place and but while gambling, you are risking to lose.
As long as you're not going to spend everything you have from that salary into gambling. I am with you that one needs to have a job or any other source of income if they are a gambler. Of course, where are they going to get that money for gambling for? even the full time gamblers now, they have started from there and they have to sacrifice some money and time for it. Until they see that they can do it full time, they're on their own. But I don't recommend one to get into full time gambling, you are for money on it still do it part time and don't be so serious with it. I know it gets to the point that we become serious from it. But the more serious you are with that, the more critical position you are getting in.