This apparent absence of thriving extraterrestrial civilizations suggests that at least one of the steps from humble planet to interstellar civilization is exceedingly unlikely. The absence could be caused because either intelligent life is extremely rare or intelligent life has a tendency to go extinct. This bottleneck for the emergence of alien civilizations from any one of the many billions of planets is referred to as the Great Filter.
Or a more reasonable explanation: it is very hard to cross interstellar distances. There could be intelligent life on Kepler 186f right now, but there is no way for us to contact them and there is no way for them to contact us.
We could design a vehicle that would go explore there (maybe using solar sails and gravimetric acceleration slingshotting around intervening stars), but it would still take millennia to get there. Maybe they sent an exploratory probe when they discovered the earth millions of years ago, but it came by 400 years ago and we missed it. Maybe they are not as developed as we are? Maybe there is intelligent life there, but they just are not interested in astronomy?