In what is almost certainly not a coincidence, Sessions' announcement came days after California's law legalizing recreational marijuana sales went into effect. Sessions' action thus runs counter to the wishes of the majority of the people in the most populous US state, as well the people of the 28 other states (and DC) that have legalized some form of marijuana use.
Federal laws criminalizing marijuana and other drugs have failed to reduce drug use. However, they have succeeded in giving power-hungry politicians and bureaucrats what was, before 9-11, the go-to justification for violating our civil liberties. The federal war on marijuana has also wasted billions of taxpayer dollars. Far from reducing crime, outlawing drugs causes crime by ensuring criminals will control the market for drugs.