... just a bemused observation.
I submitted an image to the micros of a row of spiked fence railings, taken from a low viewpoint, silhouetted against an evening sky. Diagonal composition. Very sparse, almost zen-like, with plenty of space for copy.
Shutterstock rejected it as - "
not suitable for stock."
iStock accepted it. It's gained a 5 star rating from 6 different reviewers there and has sold twice (as a small and a large) in its first week online.
Ah well ... you've got to develop a zen-like attitude in this game.