As academics, your institution is paying publishers to get access to journal (and you may loose access to electronic versions if the institution stops paying contrary to paper versions), you write papers for free, you review papers for free, you are part of the editorial board of the journal for free (or some crumbs for travelling to a conference), as an editor you spend most of your life managing people for a really…
Actually you often pay a couple thousand dollars as a publishing fee to get your paper in the journal after review. I'm sure it's not necessarily like that in every journal, but the bigger ones do it that way. So basically pay them to take your content, pay them to view their content, and do labor for them by reviewing papers for free.