Well they did a bit on the first 1. They had to make some changes, like initially Volkswagon didn't want BumbleBee to be a bug due to violence, which was what that whole used car lot spoof was for, kind of an FU to them. Megatron changing to a gun wouldn't work too well in a live action movie either. It's when Michael Bay decided to do Michael Bay things like making racist autobots, changing personalities of transformers (FU at Soundwave executing someone, and Shockwave being a bounty hunter), among many other things that it quickly became complete and utter dog shit.
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