Baseball is, by far, the hardest sport to master. Rarely do the same players stay good throughout their career, rarely do the same teams get to the world series year after year, and rarely do players keep their stats up. Their are very, very, very few that can do so, and those players have either taken steroids or are the best baseball players in the world.
The pitching aspect requires pitchers to throw 3-5 different pitches about 100+ times a game to guys they have never seen before in their life. The odds of them getting all of the players out one game is very rare; they will give up a run or two. To do that for an entire season.....impossible. An average pitcher will have 7-13 bad games a year. Not to mention they have to do this for years and years.
From the batting aspect, you have to try to hit a round object (a ball) with another round object (the bat) in which the round object is coming at you between 85-100 mph. Did I mention that the ball can curve, drop out of nowhere, run into you, and so on? The number of different pitches are amazingly effective. You haven't even seen most of these pitchers, and you have 3 chances (strikes) to hit the ball while figuring out the pitcher while trying to hit a round object with a round object while trying to see where the ball is going and how fast it is going. Great players only hit 30% of these balls. Not many players do that. Do this for an entire season for many, many years.