Bbers for the most part (not all of them but I would say a lot) before they were huge most were very insecure people. A lot got in to it to compensate for their lack of confidence whether it was to impress girls or in some cases men. A lot probably were the "unpopular" people in HS or guys that were shy that got picked on from a daily basis. From the skinny guys that wanted huge muscles to feel big and powerful to the ones who couldn't play a "real" sport most stories u hear are all the same. Dwells from "insecurities" just take a look around and they all have the same traits before they started out
A good example would be Nasser even after retirement he won't even slim down and had to be massive and take boatloads of drugs just so he can say he weighs 300 with abs 
Or kris dim almost dies but comes back and decides to compete while injecting a whole pharmacy into his body finally now paralyzed and paying the price too late
Or the countless stories of guys going on dialysis only to get a new kidney and back to shooting more drugs...
and if you were around to remember the milos/chad wars you saw an unbelievable look into just how horrific the drug use and disregard for well-being is at the top level. it's not just amazing that these guys live to 40, it's amazing they aren't dropping dead on the fucking stage.
bodybuilding started as an offshoot of olympic weightlifting and strongman exhibitions. the whole idea was that the muscled body was supposed to represent a STRONG body. the reason muscles are appealing AT ALL is that they give the visual impression that the person with all the muscles is strong. eugen sandow was a circus strongman, his flexing exhibitions (flexibitions?) were a part of a strength display. there's a reason guys like arnold and franco came from lifting backgrounds.
everyone says "who cares what they lift?" but why are muscles impressive if they can't do anything? that attitude is why bodybuilders are bloated drug sacks with SEO and PMMA all over the place, because if it doesn't matter how much it can lift, why does it matter whether or not it's even muscle? it's a body that gives the illusion of strength and power but has none. mr motherfucking olympia is in the gym squatting weights that natural gym-rats can handle. bevo nailed it here that it's all insecurity, guys putting all this effort into LOOKING powerful instead of BEING powerful.
good on capriese for getting out of it.