One good reason is that most steroids are also quite simply illegal, unless prescribed by a doctor.
Another is that steroids, when used stupidly, can have very large negative side effects, and by allowing steroids sports organizations might actually become legally responsible for athletes taking them. ("it's impossible to compete without them, so clearly the org forced me to take them by allowing them, if I wanted to be able to do my job")
Also, steroids can make a HUGE difference. You, as a bodybuilder, should know that... with steroids you can break barriers you'd otherwise never break.
__________________
/(bb|[^b]{2})/
|