Volunteer scientists do not do the curation. They do editing and peer review, but they don't do the editorial work of deciding what articles are published, how they are presented, what's featured, etc.
What exactly do you mean by curation? Editing and peer review IS what determines what is published in the journal. If the paper passes those, it gets in-- Elsevier and Springer do not make a habit of telling editors-in-chief, "sorry, this paper you accepted doesn't cut the mustard". As for what is "featured", the order in which papers appear, etc., this is negligible even if the publishers do decide it (probably not), since journals are not like newspapers, not intended for cover-to-cover reading.
E.g. if I type "economics of deflation" into Google, I get: wikipedia, a youtube video, "tutor2u.net", and investopedia among other things. Businessweek and the Economist show up on the bottom half of the first page. The first several pages of results are full of Austrian and Mises gibberish--lot's of "counter conventional wisdom" sites. This is why I don't go to Google to research economics. I don't trust it to pick quality research.
So where do I turn? "tutor2u.net?" No. I have no idea whether they can be trusted or not. So I use signaling and proxies. I look for things that have "Harvard" or "London School of Economics" domains. The folks at Harvard and LSE long ago figured out that basic dynamic, and that's why they use their names to publish journals. Is it a hard job other people couldn't do? No. But the journals exist because we trust Harvard to do the job, and we don't trust "tutor2u.net".
My wife actually hates the NIH open access policy for this reason. She argues a lot on the internet about pediatrics/child birth. She gets crazies who peddle crackpot theories by citing to sketchy papers that happen to be hosted on an NIH domain. They assume that by hosting those papers, NIH vouches for the content in those papers, but of course that's not the case.