Strategy doesn't only mean how to win the game. It can be a strategy where you take advantage on the casino when you already win some amounts. Or having a loss limit and not just spending money until you win. Gambling is mainly a game of luck and not a carreer to depend your future on it.
Not "mainly" since there are games that don't entirely depend on luck.
There are also games that don't depend fully on the luck of the gambler, there are games that depend on the skill, knowledge, and experience of the gambler. The most popular example of this skill-based games is sports betting and the most popular casino game, poker. It is true that it can't be a good career so people better choose their career better.