There are two types of gambling.
The pure gamble is a game such as the lottery or roulette. The player cannot use any skills or knowledge to affect the probability of a successful outcome, only its size. So in a lottery you can buy 1 ticket or 1000 tickets but you cannot use any knowledge to select any ticket which has a better probability than any other ticket of winning. This is very different to trading.
Other types of gambling also have cash prizes but the player’s skills and knowledge do affect the outcome. Those with more knowledge of horse racing tend to win more than novices. Better poker players win more than new players. They are able to use their skills and knowledge to give a better probability of them winning.
This is similar to trading. Better traders have greater skills and knowledge than new traders and tend to make more profits. They can still lose money and it is a matter of luck whether some trades are winners or losers, but this is business, not pure gambling, and the success of the business is based on skills and knowledge, not random good luck.