User blog comment:LDR/Possible Reaper Motive/@comment-4737548-20120224162854

Salvation through destruction. Some other cause makes species go extinct, something that could threaten even the reapers, thus they "save" the species' essence in a reaper, saving them and preserving the reapers against said unknown force. Maybe there isnt one and it was simply a program glitch in the original reaper?