Also remember that in this cycle, at the 11th hour they switched their focus from the council races to humanity as their favourite choice for reaper dreadnought-hood (one assumes the Asari or Turians had previously been the prime candidates.) So going pretty much straight for the largest concentration of humans in the galaxy makes perfect sense, since that's really all they're after.
Ah, yes. It's the "Humanity is special" trope completely made up just to put even more emphasis on Earth and humanity that still doesn't make any sense. If humanity is so uber special that Reapers can create a super incredible reaper (which can be destroyed by three people in it's early stages), why do humans make the worst Husks?
Also, if the Reapers want to use us for making more Reapers, why are they killing us by the millions instead of developing methods to incapacitate us like they did with the Collectors? Are you honestly implying that just because Mordin developed a counter measure against the seeker swarms that the Reapers decided to give up on the whole thing entirely instead of making more powerful seeker swarms? Why do the Reapers use dead corpses? Don't our bodies rot and decompose after we die? At least the collectors thought of that when they took us unconscious.