There are some great games for DOS, like Little Big Adventure for example. But most of them can be played using DosBox AFAIK. I really see no reason to keep FreeDOS alive.
There is still a need for an updated DOS system for some legacy hardware. For instance, many retail outlets still use DOS based hardware for handling purchases, although I admit this is something I have been seeing less and less of recently.
Of course, the main and best reason for having it is simply because it is so god damn cool.