Even if we do manage to achieve interstellar travel, the Doomsday argument has a "many worlds" application to account for the possibility of multiple advanced civilizations, meaning that any alien life with the presence of mind to build interplanetary flying machines is just as likely to have an equally finite lifespan. So there is a very real possibility that our historic first visit to another galaxy might yield nothing but a bunch of big-headed skeletons and about a zillion gallons of wasted rocket fuel.
Aliens May Not Exist at All
The Rare Earth hypothesis, put forth by two scientists named Peter Ward and Donald E. Brownlee, suggests that since the development of life as it is on Earth was the result of a laundry list of geological and astrophysical events so cosmically random yet so crucially specific down to the smallest detail, it is ball-smashingly unlikely for a comparable civilization to have come into being anywhere else in the universe. That is, while some kind of bacteria or algae or cosmic mushroom may exist underneath some rocks on some far distant planet, the chances of there being another race of intelligent and industrious living things are about the same as you winning the lottery every single day for the rest of your life and then dying on the morning of your 200th birthday after getting struck directly in the face by Doc Brown's time train.
While breeding a Shiny Ponyta.
First of all, the position of a solar system is vital -- if it's too close to the center of the galaxy, everything will get melted by supernova radiation, but if it's too far along the edge of the galaxy it won't be able to support life. Then, the star at the center of the solar system can't be too old, too bright, or too big, otherwise complex life won't develop (complex life is very fussy). Finally, the planet on which said life develops has to be in a perfect orbit. In Earth's case, if the orbit was 5 percent smaller or 15 percent larger we would all freeze or burn to death, respectively. The size and location of our moon keeps the planet on a stable axis, preventing rapid and cataclysmic climate changes -- if we didn't have exactly one moon of the exact shape and size orbiting at its exact distance, we would all be superdead (and likely would never have existed to begin with).
The sequence of geologic eras even plays a crucial part -- if the Mesozoic had occurred after the Cenozoic, for example, the exact conditions needed for human life to develop might never have been met, upsetting the evolutionary order and resulting in a race of dinosaur humans.
Broadcasting "2 Girls,1 Cup" into space also hasn't helped.
Even the other planets in the solar system can have an effect. For example, Jupiter plays a huge role in keeping us all alive because it acts like a giant defensive lineman, blocking us from cosmic debris and world-ending asteroids like a celestial Olin Kreutz. There are innumerable other variables, all of which played a part in intelligent life appearing on just one planet out of an entire galaxy. The odds of every one of those things falling into place in the exact configuration necessary to duplicate both the existence and success of human beings are virtually nonexistent. Therefore, the fact that we haven't made contact with any alien civilizations is probably because there isn't anything out there to contact.
Allow us to crap all over more of your dreams in 6 Reasons Space Travel Will Always Suck and 7 Awesome Super Powers (Ruined by Science).