Why do grapplers...

not grapple when they face one another. Two strikers are guaranteed to stand, but when two masters of JJ face one another, they choose to stand. I can understand that there's some sort of implied respect for their art, but if you train and fight to be the best, why not test yourself and see where you stand?

Is the humiliation of being submitted when you're a black belt that big a deal? Strikers take the risk of being kod, why can't a grappler take a similar risk?

Most recently i'm thinking Aoki/brazilian guy, Werdum/NOgueira.

Well, in the 2 examples you listed, the guy who was the inferior grappler (Aoki, Nogueira) felt they were the better fighter standing so they opted to keep the fight there and win. Aoki did that to less effect, but Nogueira effectively boxed Werdum's face, so in both instances it ended up being a good gameplan.

Well.....everyone wants to strike these days except GSP.