well in the interview I gave on the last page, Orci said it was because the allspark brought the machines to life as souless, primal transformers. then again he later goes on to say that reverse engineering from Megatron might've had something to do with it, so who knows.
who's to say they're all evil though. xbox360 just sprung legs and didn't really attack anyone. the escalade just came to life and wanted to hug the first person it saw as a thanks for bringint it to life, and mountain dewbot was just using aggressive marketing tactics.
It's my ILLUSION!