You're a fun kind of person......I could tell right away???
You didn't spend a long time thinking about this - did you? Clearly the biblical accounts related to the start of life are BS - no additional thought was required. However, if I had a few moments on the toilet to ponder this (I wouldn't) my conclusion would be that Eve was biologically created to nurture life in a way that can't come from a man's rib. She may have come from Adam's rib (just kidding) but babies need more than that - the biblical creator might have realized that.
Because religion and the words of men written in the bible are bullshit. That's why.