Why don't jet packs exist?

With all of the renowned technological advances made within the last few decades, many people have sought to create a jet pack for commercialized use. However, although prototypes have been seen, it has been met with relative failure. This is due to the materials required to reduce the weight. Gravity creates an acceleration downward, while the thrust of the jet pack would attempt to create a net force upwards large enough to counteract this force. Unfortunatley, the heavy mass of the person prevents the equivalent thrust to be achieved with materials inexpensive enough to mass produce them. Its too bad too; I always wanted to see a real-life Turbo Man.