Fair enough. And on that score, our dinky EM output (TV, radio, etc.) degrades sufficiently at about one parsec that we are probably background noise at best....
True.....another possibility is that they know we are here...but we are persona non grata....or off limits...
This could be because we are like you say a zoo or preserve....but another possibility is that we have done something in our ancient past that is so hienous that it has put us on a galactic shitlist...