Why Can't Most Catchers Hit?

Why are so many catchers in baseball so useless with the bat? A staggering 314 catching seasons of 100 plate appearances or more have occurred in the last ten years with a catcher having an OPS+ of 80 or less. That's an average of one per team for every season in the last ten years (30 teams times ten seasons). For comparison, 174 such seasons have occurred for shortstops, a position with a lot of other bad hitters. In that same time span, only 155 seasons of 100 plate appearances or more have occurred with a catcher having an OPS+ of 100 or more. That's an average of one for every two teams for a decade. To put it another way, for every one catcher that had an OPS+ of 100 or better, two had an OPS+ of 80 or worse. Why? To see how much futility is out there makes it understandable when good hitting catchers are paid enormous sums of money. Joe Mauer was given a huge contract not because he was a good hitter but because he was a good hitting catcher. Jorge Posada was paid ha...