Why do people ask "how come" when they mean "why"?

I think "How come" is a colloquialism, and I've never been very comfortable with it.

Is "how come" short for "how did ___ come to be"?

I always wonder why people just don't ask "why".

"How come" just doesn't seem to make much sense when someone is really asking "why".

they have the same meaning...

how come?

phrase of come

1.

informal

said when asking how or why something happened or is the case.

"how come you never married, Jimmy?"

I guess it's just another way of saying it . It sounds less interrogating and more casual.