User blog comment:Garhdo/Why the Reapers attack Earth/@comment-1074875-20110102131055

I don't remember the assignment on Eletania, but why go that far? The Protheans left a data cache on Mars (we can speculate on the reason, but it is unimportant to this discussion) what means that the Citadel had some kind of record on humanity.

The Reapers have a reason for their "cycle of destruction" - from what I understand they destroy everything that does not conform to their version of perfection.

Regarding the Citadel database: the Reapers don't need much, only to log on to the extranet (same as logging in to the internet today - every piece of information you desire is located there).