Because it's worked once, so why not again? It's not like the action-and-boobs addicted people who will make up most of the non-TF fan audience will care.
Sure, it might be a bit
fun, but I can't believe that anyone who is a TF fan and cares about the story will be able to appreciate another
Megatron return instead of something original and interesting.
I'll bet we'll even get a Force Ghost of The Fallen that will guide Megatron, and Optimus will die of shame because his paint job gets scratched up, and Sam and his next busty girlfriend will need to go and find a wierd faux-Lovecraftian-looking Cybertronian Mcguffin along with some foul-mouthed Autobots, and then use the Mcguffin to give Optimus a new paint job and resurrect him so that Hasbro can sell more Optimus Prime toys. Then Optimus will rip Megatron's face off and throw it INTO THE SUN
, but SPACE ROBOT MAGIC
will let the head survive until the next film so that he can be resurrected again, just like how the depths of the ocean was supposed to crush Megatron's body to uselessness in the first film's ending.*End idiotic, hate-laced anti-movie rant*
Alright, that was full of assumption and the film probably won't be that bad, but boy was baseless ranting fun.