Okay... once again, I'll give two answers.
answer 1: 'cause we don't have the tech yet (heck, so much for reaching the speed of light . We are still trying to figure out how to get to mars within a decent amount of time of somebody's life.)
answer 2: This is the long and boring answer.The big fat scientific lecture (though it's actually not that long. But anything that's boring seems long). Okay, so as something increases in speed, it's mass also does, though at the speeds usually witnessed on earth, this difference in mass is too small too notice. But at, say 1/2 the speed of light, the increase will be noticeable. and the more mass something has, the greater amount of energy is needed to move it. At the speed of light, one would actually need infinite energy to move an object that has mass. This is why only photons, which don't have mass, can go at light speed (I can list a few more, but that would make this TOO boring.) Well, now that you read this, aren't you excited for all the lectures that I am sure you will hear later in life? (whether it be a lecture from your spouse about why the children aren't doing well in school, or a lecture from a professor about quantum physics) I am sure you are.
Question: Why did I just bother to write all that down, when even I barely know about any of that stuff?