People seem to forget why the Reapers are hyper-focused on Humanity and on Earth (Humanity's home world). And whats worse is that these are likely people who did in fact play the first two games.
The Reapers have a hard-on for Humanity because they're fucking pissed at us. In their own cold, robotic way. It has been a human, or aliens under the control and direction of humanity that have been fucking up their plans for the better part of a decade now. In addition, the only group in the Universe that has definite concrete information and contact with the Reapers, their abilities and what they're up to are the humans - all the other species are either ignorant or don't believe humanity.
Oh, and we blew their shit up twice. They're not happy about that either.
So naturally, Humanity is pretty much at the top of the "Elimination List" and thus why the Reapers would be attacking Humanity so hard. (They are of course, also attacking the the other species as well, but not as much) Attacking Earth, as the center of human power, would ensure that the most damage (psychological and material) is done as quickly as possible. The Citadel would have to wait until later, since now that it isn't under Reaper control its essentially the biggest, toughest fortress around for organic/Geth life and would require a substantial amount of effort even by Reaper standards to take.
It makes sense people. You just don't want to make sense because you want to be contrary.
