You've been reading tvtropes, I see 
Though that does make sense...
True, I have, but that's not how I arrived at this. See, the reapers were building a human reaper in ME2. They used the Collectors to abducting human colonies. What was the purpose of this Reaper? Was it: 1) to try to let all the other reapers in again so they could kill everyone? OR 2) was that part of the Haestrom plot where the Geth might have been creating a wormhole inside the star to let the Reapers in just in case the Collectors failed? OR 3) was it because they thought that humans had the finest DNA in the galaxy available for processing Dark Energy and if the Collectors had been successful, everything would have been hunky dory and there wouldn't have been a need for an invasion at all! That one 2 km Reaper would process all the Dark Energy that the mass relay system produced via the process known as Space Magic.
They only needed to abduct a few million more humans, but Shepard screwed it all up! And the Geth weren't ready either because Shepard screwed up that as well by killing the Heretics or rewriting them! So they had to invade by the Alpha Relay.
It was a good thing they started flying that way three years earlier... just in case, right Mac? But then they changed their minds and decided that it was all because of synthetics. Yes. Synthetics!
See with Dark Energy there would be no reason to reap the entire galaxy. Just humans. Just Earth. Why attack the Batarians and the Turians. I mean just hit Earth. The Council wouldn't do anything. lol. Build your reaper to suck up the dark energy and go home. See how special humans were? But with synthetics it's different. Everyone had them. And there were the Geth! So they now had to send in a bunch of synthetics to kill all of us so we wouldn't build synthetics that would kill us.
Understand now?
But really humans are special. That's why they had to take lines away from Liara and make her sound like she suffered from the Asari version of Alzheimers at times. Forget she asked you if you wanted to pick up where you left off in your LotSB relationship, then immediately friend zone you. Be useless as a SB because those lines went to a human because they made humans smart like James, Anderson, Hackett, Shepard, Joker, The Illusive Man, Udina, Ashley, etc. Come on, they had to give humanity a break. So they gave the lines to Traynor. We had to have someone with over a 90 IQ.