User blog comment:Garhdo/Why the Reapers attack Earth/@comment-2256917-20110212052854

Adding to Spart's initial statement, one could say that the Reapers would've known of the existence of humans on earth when they came to wipe out the Protheans. Why not preemptively strike (or enslave and re-purpose) at that time, if all they needed to know was the location of highly evolved or "rational" animals? (Unless we assume that by then the Charon Relay had frozen over). Such a fate seems to have befallen the whoevers from Aphras, even though they were merely in a Bronze age.

In any case, the real problem seems to be that, as Sovereign said, we don't know the cause(s) for the sake of which the Reapers destroy, or are in any way concerned with, organic beings.