it's a lifestyle
Exactly... it's not a sport, it's something you live and breathe, 24 hours a day.. it changes the way you eat, sleep, prioritize your day and so on. Besides it can't be classified a sport, according to the dictionary, a sport is:
a) Physical activity that is governed by a set of rules or customs and often engaged in competitively.
bodybuilding while it may be competitive, is not a physical activity... standing oiled up on a stage, flexing is not a physical activity.