Why use attributes instead of cookies from request objects

I'm sorry if this is a dumb question. I just finished the Using Filters And Request Attributes video and watched how Craig set an attribute for each request that is handled before any response or request. Here is the code:

before((req, res) -> {
            if(req.cookie("username") != null) {
                req.attribute("username", req.cookie("username"));
            }
        });

We then refactored our code so that anywhere the request's "username" cookie is called, it now calls the request's "username" attribute.

I think I understand Craig's code, but I don't understand the advantage of assigning the "username" cookie to the an attribute before each request. Why can't we just call the "username" cookie in all of our code instead of assigning the cookie to an attribute and then calling the attribute? It just seems like the longer road to me, but I'm sure I'm not understanding something.

Thanks for your help!