It would be helpful if DT had a list of images that are overloaded in its directory so they don't really want any more. I just had an isolated beautiful rose with a bee rejected because there are too many already.
A healthy habit (besides eating tomatoes without shooting them first...) is to research the topic of your shots before submitting them. There are 105.224 rose-images in the database. If you truly believe your image can compete with the bestsellers, by all means, submit yours! But if you're not that sure, think again ;)