I'm not sure I understand your question. Do you mean, why can't you see the stars that lie beyond our galaxy from the earth? Or do you mean how come you can't see the stars if you are in outer space?

I'll assume you meant the first one. When you say "outer space", how far away do you mean? Do you mean beyond our galaxy?

It is true that most of the individual stars that we can see are within our own galaxy, however some of the bright objects that you see when you look out are not stars, but groups of trillions and trillions of stars that are so far away, that without a telescope they look like points of light to us, just like stars. Some of these objects are "globular clusters". To your naked eye they look like stars, but with a small telescope, or even a good pair of binoculars, they look like cotton balls of light. They are actually groups of very old stars, held together by gravity, about 100 billion or so stars. There are a number of ancient globular clusters that seem to be orbiting around the center of our galaxy.

You can find them in the summer, on a clear night, when the constellations Scorpius and Sagittarius are in the sky towards the west, in the early night time hours. (You could see these now, but you'd have to get up around 2 or 3 AM!) If you look right between Scorpius and Sagittarius, you are looking toward the center of our galaxy, and if you look in that direction it is a good place to hunt for globulars. So that is one type of bright object outside our galaxy, in "outer space" that you can see from the ground.

You can also see other galaxies - again, these look like stars to the naked eye, but with a telescope you can tell that they are galaxies. Occasionally, we can actually see a single star in a distant galaxy that is when a star explodes into a supernova. At that moment, that one star is as bright or brighter than the whole galaxy! Supernovae stay bright for a few days to a few weeks, as the light from the explosion slowly fades away. Mostly, you need a telescope to see these supernovae (that's plural for supernova, since "nova" is a Latin word meaning "new"), but occasionally people can see them with their naked eyes.

A recent example (but probably before you were born) is Supernova 1987a - that is, the first supernova found in 1987. That one was visible from the Southern Hemisphere, from the ground, without telescopes.

Other examples in history are Tycho's supernova which occurred sometime in the 1500's and was visible in the Northern Hemisphere, and a supernova that exploded around 1000, which is documented in ancient Chinese records and rock paintings of Native people of North America, as well as in some literature from that time in Europe.

Also, the Hubble Space Telescope can see many more stars than we can see from the ground, because there is no atmosphere in space to make the stars blurry or dim.

Now, if you meant in your question, how come you can't see stars if you are in space, the answer is you can see stars from out there. You can see many more, in fact, than you can from the ground! And, you may even get to go into space in your lifetime!!!