The discovery of new planets and new solar systems has increased tremendously in last 20 or 25 years, mostly after the successful mission of hubble telescope.But, our scientists are fail in searching alien life in any planet till now. Instead of these, there are many reasons , why we can’t find them.
First our earth maybe unique in every way including habouring such complex organisms such as us. There maybe very few planets in our galaxy which can habour complex organisms.
Second reason would be that they might be extinct. If we assume that the other life form is highly advanced then the only reason we cannot find them would be either they died due to war between themselves or they overused the resources of their planet due which again they were annihilated.
Third reason would be that they are very far away say 200 to 300 light years. Our only way to communicate to extra terrestrial life is by using radio waves. But using radio waves to send messages was devised only 30 to 40 years ago. So if we had send a message say 40 years back then that message would not have reached.
It is more likely that they have found us but do not care because we are far behind in the technology that they didn’t found anything relevant in us to contact. They are everywhere, but they are invisible to our technology.