People rely on a dictionary to be accurate...
... and the dictionaries have abdicated. That's a big part of the problem. Dictionaries now mostly consider themselves to be not prescriptive but descriptive - listing not what is correct but rather what well-known people say. Authorities like Ethel Merman. And Art Linkletter. Webster's Third - way back in the 1960's - cited both of them, and also gave "uninterested" as one of the meanings of "disinterested."
Things haven't improved much since, as you see.
Scrabble player's lament: "Whom are you going to believe - me or some strange dictionary?"
