A number of my photo's has not been accepted due quality reasons - can you explain why?

It's rare that we get to see such nice compositions here. However, I'll limit my remarks to this photo only.

I think the exposure is a little uneven.  The sky is washed out and lacks much color vibrance. Foreground shadows may need adjustment too. Check your white balance for too much blue. And it's tilted slightly to the left. Straighten horizontal lines.

It's a good photo. I think with minor corrections, it will be accepted.

Hope that helps.