Or, more likely, civilizations more advanced than us have long since stopped splattering radio waves out into the cosmos willy-nilly, just like we stopped back in the '70s. I think it's funny that our hopes for detecting extraterrestrial intelligence are predicated on monitoring the hydrogen line with a small, underfunded, scrappy network of volunteers that have only scraped enough cash to do large-scale broadcasts on that same line a handful of times in history... yet we assume that these aliens are wholeheartedly focused on blasting out constant 10 PRINT HELLO WORLD on that same line just in case we're listening. That we don't consider alien intelligences to be every bit as disinterested in us as we are in them strikes me as narcissistic hubris of the first order.