Reasons for MLB Players

Furthermore, MLB owners have enjoyed high double-digit return-on-investment for many years. By showing teenagers that steroids are not the cool nor healthy way to become more physical fit, they finally have the opportunity to show the world that they are not all Montgomery Burns (Saving the Puerto Rican League).

If most people believe that the way to get ahead is to work hard, then most people will work hard, and more wealth will be created. On the other hand, if people believe that wealthy people should not have to work, then people will attempt to gain wealth without working, leading to a zero-sum economy. If most people expect public officials to be honest, then dishonest officials will be identified and punished" (Reforming Our Beliefs Concerning...

This would actually prevent teenagers from using steroids to become more physically fit (Politics). Teenagers usually follow the images of celebrities and because of the MLB players want to take advantage of that.
References

Steroid Use in Teen Athletes. http://www.***.ca/lib/essay/69_4.html

Saving the Puerto Rican League. http://sportslaw.blogspot.com/2007_08_01_archive.html

Reforming Our Beliefs Concerning Health Care. http://www.tcsdaily.com/article.aspx?id=062107A

Politics. http://grg51.typepad.com/steroid_nation/politics/index.html