Could you explain why "the bee's knees" comes to mean an excellent suitable person or thing?

It's very hard to say why slang becomes popular. However you should know that this slang was popular many decades ago. I sometimes use it to be funny (along with "the cat's pajamas"), but don't try to use it as modern slang or people will laugh at you and ask you where you found this old piece of language.

Hi, Sir...
Nice to get your explanation again.
Thank you for the direct ,useful advices.

Best regards
From.Eric from Korea.

Hello Eric,
I'm glad you found it useful.

Please note that I am not a "sir" and there are many other members of this forum who are also female, so simly "hello" or "hi" is okay.

Grammar GeekPlease note that I am not a "sir"..

You sure do speak like one.

Grammar GeekPlease note that I am not a "sir" and there are many other members of this forum who are also female, so simly "hello" or "hi" is okay.

You got it.
I hope I'd see you next time.
Take care.

AnonymousGrammar GeekPlease note that I am not a "sir"..

You sure do speak like one.

Do you think that only men can speak correctly and authoritatively? That's rather offensive.

(I am also not a "Sir.")

This is probably from euphony, bee/knee, and that fact that bees are good creatures, in that they make honey. These slang terms come and go, and are sometimes resurrected after going out of style. "Bees knees" was apparently resurrected about a decade ago, and is still being heard. This may have to do with environmental awareness, as bees are good for the environment.

Other recently

This reminds me of the scene in "The King and I" where Anna asks why everyone calls her "Sir." The answer is "Because you scientific -- not lowly like woman."