Rejection reason

They did not like the crop. It was either not close enough or to close. You did not focus on a single item like an engine, flaps, cockpit winglet etc. You just did an awkward crop of your photo or took an awkward photo in their estimation. Show more of the aircraft next time or take a tighter shot. Being so dark did not help either lol. Don't worry. Keep on shooting :-) The "motive" comment is because they either did not know what you were trying to show or they think you could do a better job of capturing it is all.

Cheers from Canada