The “gateway” drug thing was taught to me through DARE in the 90s. But has been confirmed propoganda for decades. Calling Cannabis (marijuana is not the proper name) a “gateway” drug is like saying water or air are “gateway” drugs. Sure, a crack head has probably smoked weed, but that isn’t what got them into crack.
I would guess that these materials are, either, very old or they categorize cannabis differently because it is so common. It doesn’t help that it is illegal in half the country and legal in the other half. So any state with cannabis not, at least, decriminalized will still have the talking points for the 1930s.