I think that is the most important part of the fantasy. I haven't read the books nor seen the films, and have no intention of doing either in the near future, so I will assume that your description of Bella is accurate.
If Bella is, as you state, "uninteresting" then she services the fantasy of sustaining an interest to men who are not only impossibly handsome, but immortal as well. Edward and Jacob are Greek gods with fangs and fur, who are competing for a woman who is apparently unremarkable.
Are most women remarkable or unremarkable?