Ya, it had started as Only for writers but things have changed alot. For ordinary visitor, there is still nothing much for him since most of the articles that go there are for marketing/link building.
Ezinearticles often shows up high in the results for search engines for a wide array of topics, so it provides people with information every day (that's the whole point). You have an understandably biased view since you're a webmaster, and you pretty much only use it to promote your sites. Average internet users are exposed to EA every day due to the wide amount of articles it has in its database. So it definitely has a few different purposes
It's the same as asking why do writer write books. Infact, EzineArticles was modelled for writers only until marketers and webmasters discovered its potential. Ezines is often top in search results because it is known to have content from the "toppest" writers.
Without a website, it seems pointless to use EzineArticles to drive traffic. That is if you do not consider a squeeze page as a website.
Well, Non-Webmasters would be the readers and potential visitors of those of us who use it for marketing. For example, I've searched things like Colorado Ski Trip and have found articles on the best places to go skiing there. At that point, it wasn't about me marketing my site, someone else was marketing theirs to me. Google seems like like ezinearticles.com pretty well.