I don't know why... maybe the proportions are slightly out... but the car mode to me just doesn't look like the curved "Herbie" VW beetle. Looking for some images of the real beetle car (here, here, here), the car seemed to be more rounded, like a rainbow from the windshield to the back bumper, but the MP Bumblebee has a flatter top, so it makes it look longer.
Maybe it's just an optical illusion on the full-scale car.