It's hard to know why he wouldn't - he conspired to have people killed, and facilitated illegal activity, i.e. the sale of all sorts of drugs. You might be saying "well, drugs shouldn't be illegal", or even, "well, conspiring to kill people shouldn't be illegal", but they were illegal at the time.
Seems like a legal slight-of-hand, and also unjust and unethical and absolutely ripe for government abuse.
He was punished for the crime of attempting or conspiring to commit murder. Without ever having been found guilty in a trial by jury of his peers determining beyond reasonable doubt that the facts met said crime.