I'm not convinced that 3 full time staff is barebones given that the writing and formatting is being done by the authors, and that a solid chunk of what normally falls under the editing umbrella is being done by peer reviewers who are also unpaid.
Even if that is a fair representation of the cost to the journal to get the article published, that would mean they would break even, maybe even earn a profit purely on the submission fees. Never mind that multiple universities pay hundreds of thousands of dollars to subscribe to the journals.