Why don't fat people just redistribute that mass to get buff? I'm sorry but we don't really know how this kind of thing works amongst bots. It could be something simple as choosing that form... or may have to to with his innate programming, how he was built, age, or some other process. I don't think they'll ever address the fatness thing on film (that would be rude.) It's no less probable than him looking buff and probably more likely overall; why do giant alien robots have forms resembling ideal human forms, anyway? In a meta sense, why must designs always be an athletic build? They don't necessarily work like humans, so they don't need to look tough by human standards but be tough by their own. Designing them with different body types can only be a good thing, as it adds an extra option in details, allowing the cast to stand out more from each other. For a while, I had to distinguish Hound as "the fat one" to those not in the know, as they would take "the big one" for Optimus or "the green one" for Crosshairs. This might seem off color from someone who said they prefer humanoid designs. Yes, that's true because not only are they more expressive (which helps me a ton) but they make it easier to talk with other people about by relating features to that of humans— Me: "Remember that green one with the goggles?" Other: "Oh, yeah! Nice car, but he was an asshole." vs. Me: "Remember that big guy?" Other: "Optimus is the only one I remember, except for green guy, samurai, fat guy and Bumblebee..." Me: "Not Optimus. He was green and had a round face." Other: "Er, yah talking about Hound?" Me: "No, he has beady eyes and a round face and you can't see his mouth." Other: "I was able to see the fat guy's mouth through his beard." Me: *Gives up* (I was trying to talk about Long Haul.) But this doesn't mean that I am against the non-human designs at all. They do have their merits. They make the designs visually diverse, just like fatter/skinnier/motif-based/different vehicle based designs. I do wish the Autobots and Decepticons looked like the same species, however, with better distribution of funky bug-like features and human-like features. Now, the long coat thing, I am not sure. While many things can be explained by alien anatomy, this seems to be an outside feature but, he may have been built and/or programmed to have that as a physical feature he can't shake off. My theory here would be that Transformers can't reprogram anything that might dramatically effect their height and overall build with some mass redistribution allowed, but this is all speculation (that may have been contradicted) and probably will never be addressed on film.