I'm no expert on the topic, but Nature is an exception rather than the rule, given its history and prestige.

Academic journals were around well before the Internet. Real capital investment was required to review applications, provide editing advice, typesetting, printing, and distribution. All of those are still things, now with additional online publishing, which also has its own technology costs.

What's wild and out of whack, of course, is that peer reviewers generally aren't paid, submitters pay to get published, and readers also pay for access. Other than the relatively minimal office staff to keep things running, there's very little overhead. So why is it so damn expensive?

I think the answer is that they can get away with it. You can publish in an open source journal for free, of course, but there may or may not be quality control. Plus, it's an attention economy. If you publish in Science or Nature, you're almost certainly getting prestige that can turbo boost your career because that many people will see and likely cite your work.

And on and on it goes. I think we would pretty strong regulations to stop this system.