Bodybuilders eat plenty of carbs.
Of course, Keto is a thing, but I haven't heard many stories of bodybuilders that actually target the keto-state. It's about getting the right amount of carbohydrates (hint: not as much as most people eat).
Unless they're prepping for a contest, which is not what they spend the majority of their time doing.
Bodybuilders typically consume about ~30% protein. Where did you get the idea that it is mostly protein? Not to say that there aren't outliers obviously.
Just about every bodybuilder slams carbs, all day long.