Alrighty, my time to shine!

As stated in the link above, the batters have to essentially guess at what ball is being thrown at them, and there's no thing as a sure strike.

The bowler (Pitcher) has a lot of tools in his arsenal when it comes to tossing the ball. The goal isn't to just get the ball to the catcher, but to fool the hitter. He fools the hitter by making the ball spin in a certain way at certain speeds. He can throw multiple types of throws, such as:

• Fastball: This ball is meant to come by straight and fast, to sneak past the hitter before he can swing, and as long as it's in the "Strike Zone" it will be called a strike.
  
• Curveball: This ball "moves" while in the air, it can look like it was thrown too high, out of the strike zone, but at the last second drop into the strike zone, forcing a strike to be called.
  
• Slider: This ball can be thrown right to the catcher, but it also "Slides" side to side, so it can look like an easy hit, but as the hitter swings, it will drop out of the strike zone, causing a strike.

Using these 3 examples there are many reasons why a hitter would not swing at a strike ball, the pitcher might throw a fastball, but the batter guesses it's a slider, so he doesn't swing because he assumes that the ball will move out of the strike zone, and will be called a ball. And again, with a curveball, the batter might assume that the pitcher had a bad throw and the ball will be outside of the strike zone, so he doesn't plan on swinging, but at the last second it drops down for a strike.

It really does break down into luck and having a good eye for identifying a pitch as soon as it leaves the pitchers hand. Which is a very hard thing to do when a ball only has to travel 60 feet at 95mph (18.5m @ 153kph).

To answer the second half of your question, most every player in the game is attempting to just get on base. Very few actually swing for a home run every time.

The catch is you only get 3 strikes before you are out. also, if you hit a ball into the air and it is caught, you are out. And you only get 3 outs per inning. So the hitters have to maximize each pitch thrown at them. So, back to the first part of the question, if a hitter has less than 2 strikes and a ball is thrown at him, he has to decide first, if he can even hit it, and second if he can hit it, would it be a productive hit, one that hits the ground before it lands in a glove giving him a chance to run to first base, or, if he were to hit it, would it pop up and land in someones glove getting him out before he reaches 3 strikes.

as for hitting the ball out of play, if you have less than 2 strikes and hit the ball out of play, it is counted as a strike against you, but you cannot get a 3rd strike by hitting the ball out of play.

This adds another dimension, if a hitter is at 2 strikes, and he sees a pitch that will most likely be called a strike, but he knows that if he hits it, he will be out because someone will catch it, they will try to hit it and knock it out of play, as it does not count as a 3rd strike.

Also, as a side note, a home run is only ever worth 1 run by itself. if anyone is on base at the time, they too will count as a run, but a lone batter, with no one on base, is 1 run. in other words, you only earn one run per person that crosses home plate.