User blog comment:The Milkman/Everybody Shut Up./@comment-1341687-20120423035921/@comment-1341687-20120424180259

The Collector's base did stay. I was trying to say that. If I ended up saying otherwise, my apologies. I meant why keep hiding the fact that they were the ones abducting colonies? We don't know for certain how many ships there were/are but I don't think there was more than one. Which is why I feel at a certain point, the Collector's never would have been able to finish without the help of the Reapers. So Harbingers actions can be seen as an attrition tactic of sorts.

I also see what you were asking now, so my apologies.

They moved the Citadel because Earth is the hub for humans, the densest population. So it has the most Reapers covering it, moving the Citadel was an action of putting it in the middle of the densest force they had. They never imagined or even thought that anyone could actually manage to get aboard. The Crucible is able to latch because the Reapers are in combat with the fleets. It comes down to a moment of luck and tactics that they were even able to get the thing attached.

Why it stayed is another story. So, CB in core because of hit and run tactics, Citadel at Earth because it was supposed to be easiest place to defend and operate it in the same way the CB was used.