Why Do Teachers Make Everything So Difficult?

This little fact of teachers making everything hard has bothered me before. I mean, why don't they just get down to the point?

An example:

Today (just now, actually) I was messaging a friend and didn't know whether to use "who" or "whom" in a certain sentence. I tried to remember what my eighth grade English teacher said while we learned the difference. All I could remember though was a packet of worksheets and a long class of meaningless words that I couldn't understand.

So you know what I did? I Googled. Google.com is the most helpful resource I have come across in all my fourteen years. Simple. Easy. Gave me the answer straight away.

Why couldn't the teacher have been as straight forward and just say "if you can replace a word with 'he' or 'she,' then it is the subject of the sentence and you should use "who." If you can replace the word with 'him' or 'her,' it is the object and you should use 'whom.'"?

Seriously.