How do people get so successful with just trading?

With “so successful” you probably refer to the many “success” stories on YouTube and the Internet in general.
Don’t believe that. People who really make money are like the super rich – they don’t brag about their wealth.
Rather find someone who has made a living from trading for a lifetime. Those are successful traders.
To hit the jackpot once is not success, it’s gambling.
Success is the ability to repeat the win.