Observation: Bigger the guy, the more nude-shy?
Interesting. Consensus so far, biger dude no nude. My observations include gyms such as Golds, with smaller, curtained shower areas. Big guys don't even go there, let alone shower. But, at clubs with bigger wet areas, I've noted less size-related reluctance.
So, one variable could be size of wet area. Big guys just feel uneasy nude in small quarters?
I've noticed the same thing. I'm guessing the reasons are as diverse as the rest of our human nature. A couple come to mind though.
Body builders take great pride in the outsized muscle bulk they have achieved. If they're just average in the genital department, they don't find any pride in showing it. Also average sized genitals surrounded by a large body look small. The ego that drives body building may not allow showing anything that is just average or worse yet, small.
Body builders may also be avoiding unwanted attention. They might enjoy the admiration of other guys but get uncomfortable if the attention is perceived to be sexual in nature.