First of all, it doesn't matter how long it takes, if you keep gambling for a long time, eventually one day you will lose all of your money and not make a profit, which means in order to profit you have to withdraw your money, if you keep on gambling maybe it will take 1 hour, maybe it will take 10 years, but you will lose it all, but if you withdraw your winnings then you can stop when ahead.
Second one is that nobody can guarantee results, neither can you, if you are going lucky then you can win, if unlucky then you can lose but in the end you won't have a guaranteed idea of what you will be doing and how it will turn out.
However, not only casinos wouldn't allow that, we are talking about poor people here though. Like if you have 100 bucks, even if you get lucky, how lucky could you get to reach to like 100k+ at the very least, that would be wildly near impossible, like one in a million or even more chance. So all in all, it could be said that, you can't get rich by gambling if you are poor right now.