Two Handed Backhand
The main reason why we see so many players use two hands today is because kids start at such a young age when the wrist is not strong enough to counter-act the force of the ball with a one handed-backhand. Players, seeking an immediate fix, found that the two-hander was the solution.

Exercise:
For right-handers (reverse is true for left-handers), the best way to improve the strength and speed of this shot is by shadow-swinging only with your dominant left arm. And then shadow-swing with both hands on the grip and you will be surprising your opponent with your new power.