Gambling is fast and you will have a fast time to lose too. It will be hard for those people that only gambles but don't know how to trade. I'm a gambler and also a trader but I find it more profitable in trading because it gives me a lot of chance to earn unlike in gambling when you lose, it's hard to recover almost everything.
Trading is always an better choice to earn money in compare to gambling as in gambling sometimes you will make money and sometimes you will loose but if you have good knowledge of trading then you can make money each and every time you trade.
And what if you loose that $100 in gambling? As there are more chances of loosing money in gambling instead of doubling it as the probability in gambling is 50 50 and not every time you can win money with it so its an big risk to take as at the end of the day you will be left with nothing in your hands.