You can either have a major push with a handful of characters, or you can push more characters but not have as big a focus on individual characters.
Would it be more effective to promote, say, Superman every month for 12 months, or would you be better off pushing twelve different characters for one month each?
There are pros and cons to each approach. If you focus on one you can have a better line up of talent to focus on that character. You can't have a Geoff Johns type focusing on twelve different characters at once.