Another article asking why there aren't more knuckleball pitchers in baseball given the recent success of R.A. Dickey who won the National League Cy Young award last season. Watching animated GIFs of Dickey's knuckleball is mesmerizing, the animated GIF being the perfect form with which to fetishize the almost sorcerous movement of the pitch. Perfected, the pitch puts much less strain on your arm, allowing pitchers to go deeper in games and later into their career at near peak effectiveness. Seems like a market inefficiency waiting to be exploited, doesn't it?
I played organized baseball when I was younger, and I suspect the reason it's so rare is that it's really an all or nothing skill in both technique and results. That is, if you decide you're going to become a knuckleball pitcher, the results will be binary. It's putting your entire career in one basket.
The types of players who play organized baseball at the high school and college level are almost always the most promising players, the best athletes, and at that level, none have had to throw a Hail Mary with their career. So for any of them to suddenly try to throw the knuckleball, to take an all or nothing gamble with their baseball life, is unnecessary.
The types of people you see throw the knuckleball typically are much older, already in the minor leagues, or about to be cut from a MLB roster, and so at that point they have nothing to lose. Then the idea of trying a knuckleball doesn't seem so crazy.
The distribution of results if you have a more conventional pitching repertoire, maybe a fastball-slider combo, is less binary. There's a chance you could end up just a mediocre or situational reliever with that, but with a knuckleball, you're probably either a starter or out of baseball.
Mastering the knuckleball tends to be an all or nothing endeavor, too. It's extremely difficult to throw (I tried to learn one) and takes a ton of work to learn, let alone master. It's not thrown like any other pitch in baseball so you have to learn a lot of the technique from scratch. A poorly thrown knuckleball, to a major league player, is like tossing a softball underhand to the plate: the end result is usually the endangerment of your life, that of one of your corner infielders, or that of some spectator in the bleachers. In R.A. Dickey's first career start he gave up 6 home runs and was immediately demoted to Triple A.
That said, I do think more players who can't even make the cut for their high school team, or even fringe pitchers, should try to learn the knuckleball much earlier in life. Their career is essentially already over at that point, the risk reward ratio makes sense then, and they give themselves a headstart on learning the pitch. Even then, they'd likely have to still throw a conventional baseball alongside it for many years just to maintain enough arm strength to throw it at a useable velocity in the major leagues. R.A. Dickey's knuckleball is the fastest I've ever seen in baseball, he throws it harder than probably any of you reading this can throw a regular fastball.
A question more people should ask of professional sports is why more NBA players don't shoot free throws underhand. Given how poorly some of the key stars in the NBA shoot them (among regulars, Dwight Howard is last in the NBA right now shooting .508), the question of swallowing your pride and machismo and shooting a style that would likely improve your team's record in close games by a non-trivial number of games is one that should be asked ever year until someone does it again.
Free throws are one of the most boring parts of basketball anyhow, and I bet the first player to do it would be a huge fan attraction.