Why does one have to say : "everybody is" instead of "everybody are" ? Everybody means more than one persons, so "are" would be a more logical choice ?
***** NOT A TEACHER *****
(1) Yes, you correct: "everybody" is, logically speaking, plural.
(2) But if you carefully look at the word, you will notice that it was originally two
words: Every body has one nose.
(3) And, yes, I believe that native speakers often consider it as a plural:
Tom: Is everybody here?
Martha: Yes,
they are. (Instead of: Yes, he or she is.)
***
Mona: Everybody loves ice cream,
don't they? (Instead of: doesn't he or she?)
(4) As you know, humans invented language. And since humans are not
perfect (!), their languages cannot be perfect, either.
UPDATE: I have just noticed that I forgot to write "are" in my first sentence.
That is why the teachers remind us non-teachers to carefully proofread before
posting. I apologize.