You make a number of interesting observations, and you’re right that “Who is it for” does feel more natural, despite being the object of that sentence.

Perhaps you’re correct that some teachers taught English grammar poorly, and insisted on specific words without explaining the underlying grammar, and perhaps that failure has led to people using the language incorrectly, which has then snowballed such errors into common usage.

Another word I often see poorly used is the reflexive pronoun ‘myself’, which should be used as the object when the subject and object of the sentence both refer to the person who is speaking, as in “I gave myself a pen”, but I know at least three people who commonly misuse it with a sentence like “Make a decision and get back to myself”, which is just hopelessly wrong and sounds terrible, but I think it may be the same issue you described where people have never had it explained to them what the correct usage is, and end up mistakenly thinking that it sounds more “correct” to say the word myself in place of the word me. Credit to Austin Power’s deliberate blunder Allow myself to introduce myself