The fact that Homo sapiens is not intelligent, doesn't prove that there is no intelligent life in the universe at all. :)
So the natural question is why are we so isolated from any other signs of intelligent life ...
Mabye because really intelligent creatures would be intelligent enough to avoid meeting us. :-)
I personally would be very surprised if no intelligent forms of life were existing at uncountable places of the universe. We thought sun was circulating around the earth, we fought against the fact that evolution is the reason for our existence, and sooner or later we will have to accept that also our planet is not as special as we like to see it.
One problem (between many others) to detect (or even communicate with) extraterrestrial life are the huge distances. If for example we receive light (or electromagnetic waves) from a place which is one million light years away from us, the arriving waves give us information about the prevailing conditions one million years ago: we look into the past but don't 'see' the presence. Imagine how long a communication signal from a sender to a receiver and then back to him would last ... Of course if we are lucky we may detect life nearer in our 'neighborhood' one day. :)
Not long ago I read "The Three-Body Problem" from the Chinese science fiction author Liu Cixin which offered quite some food for thoughts - just in case you are interested.