1. Space is very, very large. 2. Traveling between stars takes a very long time. 3. Other than a desire for exploration there is no need. Resources and planets

1. Space is very, very large. 2. Traveling between stars takes a very long time. 3. Other than a desire for exploration there is no need. Resources and planets are plentiful. 4. It now appears there is only an extremely brief window during which a technological species broadcasts in a detectable way. #4 is probably the biggest problem. Digital compressed broadcasts would be difficult to detect, and by the time you have that technology you can build much more sensitive receivers and don't waste energy dumping millions of watts into space. There could be 1000 intelligent species in the Milky Way right now and it is still unlikely any would visit our solar system within the past 10,000 years, nor in the next 10,000 and we would not be able to detect their faint compressed, encrypted broadcasts.