Nice observation. Good that you decided to include the cabin after all, that's what makes the picture interesting. Only sky would be empty and boring, even if pretty. But here is the contrast between a small and rather neglected cabin, and the vastness of the sky, and, by extension, the world. The contrail only emphasises that last part.
Yeah, I avoid taking photos of just the sky. I don't find them to be very creative or interesting. Instead, I try to find scenes where I can include something in the foreground using the sky as a backdrop.