One of the aspects of designing things for these films is that LOTS of work gets rejected for all kinds of reasons, but mostly it is just not what the producers/director/whoever has in mind.
It is just something you have to learn to deal with and move on.
So here are a few recent creature designs I did for a movie that were rejected. I could have continued to work on reaching a design that was more to the director's liking but in this case I was supervising work on another project and didn't have time to revisit it.