Presumably it's related to increased conservatism in gen Z males: https://www.axios.com/2024/09/28/gen-z-men-conservative-poll . Conservatives generally have more negative attitudes to drug use.
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> Conservatives generally have more negative attitudes to drug use
That is categorically false.
I think it would be interesting to look at whether the rate of physical / sexual abuse has changed, since that's significantly correlated with use of hard drugs.