This is all common sense op. Even kids these days are aware of the fact that gambling is not a proper source of income since it relies on luck way more than skill. Few people do become successful through gambling, but they are part of the minority.
It is very possible to have gambling as a primary source of income in the professional sense. There are people that are professional gamblers. They do this for a living and earn a living from it. It takes self discipline to do this.
True, but it's still a risky gamble even for them due to the volatile nature of gambling which is why there are only some of them out there.