> I think that would be such an advantage.

It reduces reach, which is a disadvantage, and most pro players have sufficient swing power on the forehand that the second hand would be superfluous.

Of course Monica Seles utilized the two-handed forehand to great effectiveness.

On the men's side, Fabrice Santoro was probably the most famous and successful two-hander.

It's just different angles and motions and muscles from the forehand and backhand. Physiologically, it's easier to generate pace from the forehand, especially using the rest of your body. On the backhand, the second hand can give you a little extra to make up for the "awkwardness" of the stroke.