I know that I, as an author, stick to WoWI only for multiple reasons.
- one place to upload/update new versions/descriptions/screenshots
- one place to find bug reports, etc.
- one place to converse with users
- the "feel" of the site
- I don't really care how many users use my addons or how much donations I get
While there are some authors who do use both sites, there are many reasons why some authors don't.