Why is it “Who do you help?,” not “Whom do you help?”?

I happened to watch a lecturer was explaining word order of English in the beginners’ English learning course in NHK’s - Japan’s largest and publicly-owned broadcasting network – educational TV program (aired on July 23rd). He showed four cubes, each of which showing the word, “Who”, “You” “Help” “Do” placed at random, and asked students to put the cubes in the right order:

Right answer: Who Do You Help?

I was comfortable with “Who do you help (speak / give / write, and so on) too, but a question arose:

Is “Whom do you help?” grammatically wrong or, obsolete? If so, why is it wrong, how and around when it became obsolete?

I’ve never seriously thought of such question as the declension of a dative pronoun in interrogative form until I hit upon the above TV scene. Taking advantage of this opportunity, I ventured to post a beginner’s question.

"Whom do you help?" is correct. But many English speakers use "who" wherever they should use "whom".

References:

https://en.oxforddictionaries.com/usage/who-or-whom

https://www.grammarly.com/blog/who-vs-whom-its-not-as-complicated-as-you-might-think/

https://www.diffen.com/difference/Who_vs_Whom

https://www.dummies.com/education/language-arts/grammar/choosing-when-to-use-who-and-whom/

In a comment, John Lawler wrote:

They're both grammatical, but the use of whom has declined in modern English, to the point where substantial portions of the speech community actually follow different rules for its use because they use it so seldom. Since Anglophone schools teach their students nothing about English grammar (except what to avoid, for no reason anybody ever mentions), people have pretty much given it up as too much trouble. Consider: when you start a clause with whom, you're announcing that an object of some kind is coming up, though you haven't even given the verb yet. That takes a lot of processing.

It is grammatically correct. In spoken English in Ireland and the UK it is actually over-correct and can sound either pedantic or ironic. In the U.S. and Australia, however, I've been told it is more commonly used in speech.