Probably because wild rice isn't actually rice, but a grass seed. I've been thinking of using some sushi rice or other high-starch rice in a beer, because you'd get more out of it than normal long-grain rice, at least, I think you would.
Wild rice makes good beer. it is very nutty and turns the beer pink. Randy Mosher has a couple recipes in Radical Brews and Papazian has a recipe in his beer travels book.