Quote Originally Posted by Noclevername View Post
OK, say you're right. Intelligent life existed long ago, for the sake of this argument. That still leaves ALL the other obstacles I listed. Any ONE of which equals a no-show.
All the ones you listed plus many more besides !

So your explanation is that intelligent life is not very rare, but:

it either does not last much beyond our stage of technology, or they (or their AI descendants) never leave their home system.

Also they do not make any observable mark or signal of their civilisation, although they are billions of years old.