The question you might ask is why doesn't EVERYTHING travel at the speed of light. The speed of light is one in some units. We just happened to develop the meter and the second before we could measure the speed of light. These units are totally arbitrary.
Everything does travel at the speed of light. It's the only speed that exists. When you aren't moving relative to the space around you, you are traveling at the speed of light along the time axis. As your speed increases through space, your speed along the time axis decreases to compensate, ensuring that your total speed in space-time is the speed of light.
