Because unless you are an author who gets famous and writes about using drugs all the time and practically nothing else[1] no one except the police care. Everyone over 30 knows that every professional workplace has habitual coke users, that a large majority of artists/musicians/art teachers/bar tenders/chefs are currently or were previously users of weed or LSD.

[1] https://pen.org/press-clip/british-author-barred-for-moral-t...