Student or Learner
Someone asked me why "whom" is being replaced by "who" and I just answered "whom" is longer than "who", so it sounds more inconvenient, but I was not sure of the reason. In languages, some phenomena are hard to explain, but if I knew the reason for "whom"'s disappearence, it would be better.
ex)She is the girl who(whom) I like.
That's my hypothesis.