As far as I know, it was always a rule that players must adhere to federal law, and steroids were federally prohibited by federal law, without a prescription, at the time. Now, with the prevalence of uppers in baseball for decades, the question of how this should effect his hall of fame chances is a separate, debatable topic, but as far as rules, he broke the rules and so did they. But the fact that other people broke rules before him doesn't change the fact that he broke the rules. The memo was a clarification that an updated federal law was relevant to baseball players. After push back that nowhere was steroids explicit banned was what MLB to finally agree to a rule that mentioned steroids specifically. Seems like saying "Yeah bit there's no rule that we can't poison the opposing starters water bottle". Yeah, that kinda goes without having to be specifically laid out