Fluff is a licensed product. Some times a company will allow its product to be used in conjunction with another product but this doesn't happen a whole lot. Fluff basically, is a marshmallow spread. Except for the flavored varieties, it tastes like marshmallow. It's easier and cheaper to put out a marshmallow flavored item than it is getting permission to use the Fluff name.
Now, if you're talking about marshmallow in general, that's another issue.