Well, it did happen, actually.
We see one predator get taken from behind, another rush out into a corridor and witness a third predator get killed, then he acts like a dumbass and hulls the ship. Finally that predator bites it after sending out a distress call.
So, it did happen, it was just totally retarded.
The key difference between the unrated/extended cut and the theatrical cut is that we got to see the main predator ship leaving Earth orbit, then launching a scout ship (which apparently the Predalien got aboard somehow?) and then that ship goes back to Earth (for no explained reason) and crashes.
It's a mess.