I honestly don't think Tim has that great of name recognition beyond comic book/older fans, which is to say he's not recognizable to the public as a whole. Almost everyone who knows Batman knows he's Bruce Wayne, but I've rarely met a casual fan who can name a Robin (and if they can it's typically Dick). The person behind the Robin mask just isn't that important to most people.

And I do think the other four (five, if you count Carrie) occupy interesting niches that Tim does not.