>>11548858Because THE VAST majority of life is found on planets orbiting within the plasma sheaths of their parent brown dwarf stars. Earth, we, we are a space oddity, life existing on a planet the way it does here, around a "main sequence" star is exceedingly rare and demands a very unique set of events to occur before it can become a reality.
If you travelled to hundreds of thousands or even millions of "main sequence" stars similar to our Sun, and checked the orbiting planets for life, you'd most likely not find any. And if you went and checked out a lots of brown dwarf stars, you wouldn't be able to see any life either, because you wouldn't be able to see through the thick intensely glowing plasma sheaths. Nor would your radio waves or other scanning methods be useful. Most likely your ship wouldn't be able to penetrate through the sheath either without getting fucked up.
To put it simply, the reason we don't see aliens is because they're out of sight from us. And we're out of sight from them. Everyone's hiding from each other, within their own little cosmic wombs like chickens inside eggs. We could find aliens who are in the same situation as us; being on a planet orbiting a "main sequence star", but due to life existing under such an arrangement requiring a very specific chain of events to occur first, it makes it extremely unlikely for the inhabitants of two such planets to ever detect each other.
To help you understand further, more in-depth, as to why we haven't detected any aliens and why they (most likely) haven't detected us, see (note the timestamps):
https://youtu.be/mINsiT70OHE?t=1h12m52s And more in-depth: [YouTube]
https://youtu.be/Kff_ytg0-8w?t=7m31s 
