I would say that if there really were other species (As intelligent or more intelligent) than us there are only a few reasons why we haven't met them.
A. Option a is the theory that they have already arrived but are smart enough to not interfere with us for any variety of reasons.
B. Option b is that due to the big bang happening for the entire Universe, it's possible that any other species that exist are at the same level of development as us, even if we consider their species hasn't ever had to repopulate from scratch due to natural disasters (Like Humans have had to deal with) those other species might only be a few thousand years more advanced than us, which wouldn't be enough to really travel to other galaxies so easily. Remember the Big Bang explosion's after effects are still happening today. The galaxy we are in is moving at a speed away from other galaxies due to an explosion that happened billions of years ago. In other words if there are other intelligent life on other planets, you can't forget that the distance between them and us is EVER expanding which will make it even more difficult to travel to us or vice versa.
C. Option c is there are no aliens and we are the only intelligent species in the Universe.