Why is financial freedom achieved through investing rather than working?

Work gives people a false impression that every penny you earn depends on your effort. If you lose your job one day, you might find yourself in a big trouble.
Over time, this illusion becomes your creed. So you spend the rest of your life seeking out various bosses, contributing to their wealth and prosperity.
In contrast, investing can gradually train you to accept life's impermanence and earn returns amid uncertainty.
Being willing to accept impermanence is definitely a key factor in achieving freedom, not just financial freedom. You will balance your desires and realize your freedom within limited circumstances, including wealth freedom.
This is the best explanation for "Rich in strategy, not in labor."