Everyone, really?

I've been building webapps since forever and I've never cookies directly in Javascript like that and I can't, personally, think of a use case where I would do that.

I've only used cookies that store a session id and I store everything in the session. The session id cookies are handled entirely by the servlet container.

I don't believe I'm doing it horribly wrong.

What you stated is pretty normal seeming to me, so no, not "everyone". But I think web developers still need to know what a cookie is and how to use it, even if you dont use them often. They can provide a better user experience remembering some aspects of a user or their session long after it has expired. Many sites have semi-authenticated states where you may not want to hold user data, but still remember some details about their session.