How can some professional futures traders make a lot of money with 20-30% win rate?

It means they may win $5 or more for every $1 they lose.

Inversely, if you have a 75% win rate, but you win $0.50 for every $5 you lose, it will be a matter of time before you blow up your account. As you can see the win rate is only part of the winning combination.

The risk/reward ratio should be combined with the win/lose rate. At the end of the day, if you aren’t able to make good trades, the ratios and other numbers won’t really matter.