tl;dr: Pot is illegal because of the money coming in from big Pharma companies to keep it down, since they will lose money once legalization occurs. Community Anti-Drug Coalition of America (CADCA) is hypocritical in it's war against marijuana while choosing to ignore the dangers of opioids and related prescription drugs.

Also, law enforcement is lobbying hard to keep the status quo since property seizures from pot activities are a major source of income to law enforcement since the Reagan administration.

"Legalizing marijuana could, however, hurt the bottom line of drug companies that make money off drugs like Oxycontin and Vicodin."

RTFA.