The answer to all rejections ultimately boils down to lack of sufficient original high quality content. Sufficient meaning enough quantity, original meaning not found elsewhere on the Internet, high quality meaning valuable to our users, content meaning information. Sites that fail on one or more of those factors don't make it in. Some sites, by their nature, are designed to fail on one or more, others are capable of remedial work to bring them up to standard. But no-one should change their webmaster strategies to get a DMOZ listing, assuming their site is successful already. However, we would like to think that sites that do meet our criteria are the best examples of their type available and should, all things being equal, be successful whether or not we list them. Critically examine all aspects of your site against the requirement for sufficient original high quality content. Where you think you could do better, do better. If you can't do better either the site falls into the category of sites whose design and purpose will always prohibit their listing, or you are not being critical enough.