On the other side of that, if one has been banned then why would they want to leave their work up to enhance the website that banned them?
Quite so, but the fact is that in most countries you have no right to un-publish your work - to have it removed from a website once you have uploaded it, eg. It is the same as sending someone a letter: the sender owns the copyright, but the recipient owns the piece of paper, and the sender can't demand that the piece of paper be returned or prevent it being publicly displayed.
The moral of the story is to read the T&Cs of websites carefully, because some them give the owners of the site control of your content. NikonGear, to its eternal credit, does not, but when you use dpreview you agree that:
"With respect to comments or other text-based content you submit or make available for inclusion, you grant us a nonexclusive, royalty-free,
perpetual, irrevocable and fully sublicensable [emphasis added] right to use, distribute, reproduce, modify, adapt, publicly perform, translate, create derivative works from and publicly display such content throughout the world in any medium. With respect to photographic content that you submit or make available for inclusion, you grant us a nonexclusive, royalty-free right to use, distribute, reproduce, publicly perform, and to publicly display such content on the Web Site
or any of our affiliates' web sites or mobile applications [emphasis added]."
