It has a lot to do with the fact to be a body builder you have to have a certain type of body which means genetics, and also very low body fat. Another thing is a lot do work their jaws, face etc, so they also get bigger.
But also most body builders don't lift anything compared to what they have in muscle. A weight lifter that is about the same size can lift usually 2 or 3 times more then a body builder. To get those muscles it's high reps, medium weight not heavy as heavy will fatigued the muscle too fast to get those nice big bulky muscles.
I end up being a body builder coach as most of my football players want to have the body of a body builder. So I ended up having to do a lot of research into the area. Most Cathelites lift heavier then a buff body builder during a normal workout, there are a few exceptions but in general it’s a medium weight, with a ton of reps, think 50 + reps, so it builds muscle faster and gives it that huge bulk due to all the reps. As this was also taught in my Body Building Academy class, but in general you just got to have the genetics to do it.
Kit