Aliens

I am willing to accept that intelligence exists outside our range of communication ... Taking this into account, my question still stands: where are they?

You've obviously done a bit more research on the topic than I have. I don't really follow SETI nor have I looked into any broadcasts we've sent, but let me continue to play the devil's advocate here... because it's fun

First thing that I can think of is, do you know at what frequencies these messages were broadcast? I know the Sun is of type... G2V I think? This likely affects what frequencies we find appropriate for communication. The sun's spectral type is also somewhat rare, I think something like only 1/13 stars in the galaxy are of the same type. How long was the duration of the broadcasts we sent? What if the message was simply missed?

Assuming this isn't a problem and communications have a 100% success rate, which is very unlikely, then did we match up time? Remember we live in four dimensions, not three. Considering the life of the universe, the human race has occurred in what some call 'the blink of an eye' and our civilized state of being able to send/receive electromagnetic communications is a much smaller window. Who's to say that the system we've sent messages to didn't have life or won't have life sometime in the future? If civilizations happen in the blink of an eye compared to the life of the universe, what are the odds that two civilizations so close to one another will both be capable and watching the sky trying to engage in communications at the same time?

Lastly, what stars are you referring to? Obviously I'm not asking for a complete list, but a star's lifetime is inversely proportional to its mass at formation (Look up an H-R diagram if you're not familiar). So I would wager (this is a complete assumption on my part) that a good majority of the stars we've broadcast to are massive stars, and therefore have short lifetimes. It's been suggested that evolution of life in these star systems would not occur since there is not enough time. I think some of the most massive stars have lifetimes less than 1 million years? If you look it up correct me if I'm wrong as its been a while. I may be off by an order of magnitude, but either way they have lifetimes that are very short as far as stellar lifetimes are concerned. Assuming that some of these stars are capable of supporting life, what is the distance? Again, we find ourselves limited by the vastness of space. I did take the liberty of looking up the 50 closest stars to us. I think the 50th closest star is around 16 light years. So any communication with a civilization of that system would take 32 years (16 out, 16 back). So maybe some of these messages we've sent to different stars systems haven't even reached the star yet, let alone had time for a message to travel back. Who knows, right now an alien civilization may be reading one of our messages and deciding if it's even wise to respond .