A variation of “they’ve already discovered us” is this:
(Along the lines of The Toolmaker’s Koan): they are waiting for us to mature beyond competitive consumptionism. In this case, we would have to find our way past the self-destructive technology barrier and reverse our attitude toward resources (anthropocentrism). Any trade contact with ETs would be dependent on our not using their technology in a consumptive, destructive manner.
In other words, the universe is patiently waiting for us to either destroy ourselves or get over ourselves before it presents us with bigger options. If we happen to make the next level of transition (infinite energy from some new Planck-level exploitation) without learning to care for our planet and cooperate with each other, then they may step in and send us back to the Stone Age.
Big Brother is watching us, and he’s a lot bigger than anything we can imagine, and enjoys watching us destroy ourselves. This would explain a lot about why most of our gods have been War gods: we are supposed to learn from each event but we keep repeating the same behaviors (conquer and collapse).