What I don't understand is why peer reviewers agree to perform uncompensated labor on behalf of these gargantuan, highly profitable publishers. What is the benefit to them, other than the warm glow of fulfilling one's professional obligations?
What if the paper is written by Author Z, whose work you are familiar with and whose papers you read anyway. Why not review it?
And so on.
But there are other motives. Regular reviews give you some perspective that you otherwise wouldn't get. For example, you see what mistakes others make and that can help you improve your own papers. Another motivation for me is sometimes that I don't want the paper to be reviewed by someone less qualified in my areas of specialization.
Also you get a sense of power anonymously judging your colleague's work..