Because they don't seem to have an interesting enemy like Saren so they're going for the old standby of Earth being in trouble. Because we all live on Earth so therefore we're all kind of invested in it.Jeyl said:TAKE BACK EARTH
Why? What did Earth ever do for me in Mass Effect 1 and 2? I think I'll go help the Quarians find a new home or protect the Assari's home world. Earth being in danger is just boring.
They did the same with the whole humans disappearing thing in ME2. Because we're also human and therefore should be invested in saving them, I guess.