Trading is knowledge based, without having knowledge on how to use the trading sites/tools available on these sites, you simply can't trade, while on the other hand, gambling is different, as it is solely on luck. Luck runs the gambling sections, there can be some games that one will know so well, and might have received medals for it, but on the play with someone else, who is probably new in the gaming system might become a winner and everything changes.
Gambling requires luck and
Trading requires knowledge, though, there can be some cases where luck will be required to win some big fish.