Twinkies Aside,
Yes its true that they sent a signal to (presumably there homeworld), the point is, maybe it didnt just start happenin, but has been transmitting nearly as long as they have beeen here, that would mean that others were allready on the way to rescue or whatever.
Dont forget they did also have Prophet for a while, and maybe gathered a great deal of intel from the suit linkup, i also reckon that the gathered intel, anol or suit probe, make yr choice? has led the Aliens to rethink thier strategey, and go on foot so to speak, as air targets are easy stuff to handle, an they seen we get better chance on ground to hide and stuff
Clearly we owned em, with the Nano suit 1, hence the need to study Prophets suit, now remember the green jellyfish dudes in the mountain with the deads, and compare em to some of the new Alien footsoldiers,
Same dudes even with the dreads hanging out, but in a protective suit, does SUIT start to ring any bells??
My view is, it took em 3 years to adapt thier tech, and create what they presume to be a superior fighting force, so they now intend to own us and our Nano Suit force, perhaps after including some of our Nano suit tech we might even find they got some added features built into their suits also, just a thought?
Overall, ifn we had just left them alone, then maybe they wuda just been rescued, but those damm Koreans love a bit of action, hence the present conflict as we saw it develop, and got dragged into it, now we gotta deal with it and see what happens.
also they do want the twinkies, and Sesame street, and any power sources they can get, but most of all they want to ( Get Prophet Back at all cost, ) cos they liked him so much as he's way cool.

Guss