That article goes on to say that from there on out, he pretty much dominated any sport he tried. He experienced pretty typical childhood insecurities and then went on to exceptional success, achievement and fame accompanied by adoration for his looks.
Seems like there had to be something more there.
I think a lot of celebrities have insecurities because their looks cannot be maintained. He seemed to have a thing for plastic surgery.
Ken Patera thinks steroids did it

“Do I think [Kris] emasculated him? Oh, God, yeah! Bruce had no control over Kris,” Ken said. Ken first advised Bruce on weightlifting techniques while both prepped for the 1972 Olympic games in Munich, where Bruce finished in 10th place in the decathlon. After four years of intense training, a pumped-up Bruce returned to win the gold medal at the 1976 Olympics. Anabolic steroids were legal for competitive use until 1975, and Ken thinks the chemicals could have triggered Bruce’s transition! “Maybe that flipped a switch in his brain,” Ken said. Bruce, 65 – who is being sued for wrongful death over a car crash – revealed he’s changing genders in an explosive interview with ABC’s Diane Sawyer.
http://www.nationalenquirer.com/celebrity/its-all-kris-jenners-fault