Some PED's can be dangerous though or at the very least haven't existed long enough for us to understand the medical risk.
For those reasons, a lot of guys won't take them. These guys are at a disadvantage.
It's not like weightlifting, cardio, cryotreatment, massage, energy exertion tracking etc where you're talking about regular exercise and treatment that guys can choose to do or not do.
You're talking about putting foreign substances in your body that may have substantial long term risk. The guys willing to take those risks can experience significant changes to their bodies that put them at an advantage over the guys who play it safe.
All that said...baseball was much more exciting when Sammy, McGwire and Bonds had gigantic heads and bacne.