Bodybuilding has always skewed blue collar, and blue collar skews more right than left. It's probably changed a little bit over the last few decades, but not tremendously. Liberals tend to go into the endurance sports. Strength sports tend to be classed as more overt displays of manliness, and male dominance, and that's frowned upon in liberal cliques.
A guy named Carl Stempel wrote about this some in various sporting journals, if you're interested.