Because You are to pussy to breathe in?

Jus kidding :P

It's just an alternative method to smoking, I personally found gravity (bucket) bongs impractical and a waste of time, "lung" bongs however I think are pretty cool, and my non-smoking friends loved being able to get high by jus makin the smoke bypass the mouth, just straight into the lungs.

Eventually they started liking normal smoking tho

Jonny