You pretty much covered all the bases in your 5 bullet points at the end.

Perhaps there is only 1 advanced civilization per galaxy? Who knows. We are still infants when it comes to technology. We've only had radio communication for about 100 years. Not a long time in the scheme of the universe.

Maybe most advanced civilizations stopped using radio transmissions ages ago and use some more efficient, faster form? We still have a lot of secrets to unlock in the universe and more advanced ways to communicate may be one of them. Steemit was only created last year and it's one of the most advanced platforms in the world!