You are absolutely right bud, who ever claims to be a professional gambler and the same gambling isn't what is paying his or her bills, then such person is lying to himself and those who care enough to listen and believe his claim of being a professional gambler.
What about gamblers who have won big that they have enough to sustain themselves. We have heard news of people winning millions, and they can decide to stop working and switch to full-time gambling. Such people can rightly claim that they live on gambling.
This days with alot of things people can do to make money legitimately even on the internet, I don't see why anyone would prefer to become a professional gambler knowing fully well that making money from gambling is luck dependent and there day he can go on a long losing streak which may lead him into financial issues or instabilities.
It is very important for people to choose their career wisely as wrong choices often lead to regrets in the future.
Anyone who doesn't have a major source of income would end up in debt if he gambles consistently. How will he fund his gambling accounts? If he had dependents, who would he provide for in an unpredictable terrain like gambling?