With Rose, it's that it's the Hall of Fame, not the hall of nice/ethical people or good sportsmanship. Moreover, he earned it before he began cheating.
For steroid users like Bonds, McGwire, etc., again...ethics. Other steroid users are probably already in the HoF and others used greeenies. The league knew and let them get away with it, and many used steroids that were allowed until MLB and the PA instituted mandates to change that. Let them in, but make note of their transgressions, if they've been confirmed.
Except for the fact that it was illegal under US laws without a prescription.
What Rose did should keep him out of the HOF during his lifetime. He knew the punishment for betting on baseball. He is probably a gambling addict. Pete met wife #1 at a horse track.
What Bonds and McGwire and company did should keep them out of the HOF forever, IMO. They broke the law and BALCO helped them cover it up.
Notable players linked to performance-enhancing drugs
Bud Selig should NEVER have been voted into the HOF. He allowed the drug problem in MLB to continue for about 10 years with no action on his part.