Close mouthed characters.

Why do I have a character who won't tell me why he's in the book?

I mean, don't get me wrong - I love him, he is a great fun character to write, he has made my story SO much more interesting than it would have been, and I'm grateful that he jumped out of the backstory and forced himself into the role of a main character. He has lots of reasons, in terms of the story as a whole, for being there.

But I still don't know the basic reason he's actually in this place where my female main character lives. I know he has a mission; to protect her. But I don't know exactly what from (although I have a reasonably good idea) and I don't know why she needs protecting.

After 77K you'd think I'd have a clue...