First and Last Contact.

Its a big universe out there. Jo Walton at Tor has an article on this, asking, if we are not alone in the universe, why are we alone so far?

The science fictional answers to the paradox are:
The aliens are keeping a low profile (Ken MacLeod’s Engines of Light)
The aliens are benevolently waiting for us to be mature enough to meet them (Heinlein’s Have Space Suit Will Travel)
The aliens are too advanced for us to notice them (Carl Sagan’s Contact and in Clarke’s 2001)
Earth is a preserve (David Brin’s Uplift books)
Earth is a recruitment center (Jerry Pournelle’s Janissaries)
Earth is a meat locker (the movie SIGNS by M. Night Shyl)
Earth is under quarantine (C.S. Lewis’ Out From the Silent Planet)
Advanced Aliens go into the singularity and don’t care about the outside universe any longer (Verner Vinge’s Marooned in Realtime)
Space is big, and there aint no such thing as a ftl drive, Virginia (Larry Niven’s Known Space, Le Guin’s Ekumen)
Aliens are warlike, and kill each other off (Fred Saberhagen’s Berserkers)
Aliens are just too alien to care about contacting us.
Intelligent life is just too rare, and the chances of surviving long enough without natural or manmade disaster just too small to allow for contact (any number of sf authors, starting with Olaf Stapledon).

Take your pick or make up your own. One of the factors in the so-called Drake Equation has to be very low: either not many stars have planets, or not many planets have life, or not much life is intelligent life, or not much intelligent life is civilized, or not many civilizations want to make the effort to find us, or the distance is just too far, the time involved just too long, the effort too great and the rewards too minor.

Myself, I like the answer in Greg Bear’s Anvil of Stars, and also in the Spider-Robinson fixup of Robert Heinlein’s Variable Star: the aliens are warlike, and First Contact is always Last Contact, because they kill off young technological species before we can form a threat to them.