What are the differeces between 'why' and 'how come'?

Question

So, I am kinda confused when do people actually use 'why' and when do they use 'how come'?
Which one do YOU use and under what context?

I know that people use these two interchangebiliy. But I am sure that there are some context in which one is used and not the other. Please use your intuition in using English as a native speaker and give a good guess why one and not the other. I mean the mere fact that 'how come' is not used very often points to some differences.
Thanks,

Answer 1

"how come" first appears in John Bartlett's 1848 Dictionary of Americanisms, one of the important early books dealing with American slang and colloquial expressions. Bartlett's comments suggest that it was in widespread use when he wrote it.

This expression derives from "how did it come about that.." and has shortened to "how come"

Answer 2

There is no difference they are the same thing. There is no grammatically correct way so saying it both are acceptable.

Answer 3

they are understood to be the same thing, but using "why" is more formal. you wouldn't ask "how come" at a business meeting or something like that.

Answer 4

To me there is no difference in the two. I use both.

Answer 5

It's primarily level of usage. "Why" is more formal, "how come" more colloquial.