> I know people see this as rent seeking, but journals DO provide a service which costs money.
I don't know the specifics of Nature, but the main service provided by journals (peer-review and selection) is usually done by other researchers that are unpaid. Most journals will do little or nothing about typesetting and edition of articles.
What journals do is stand in the middle of a system where researchers need to publish in high quality journals in order to advance their career and also need to access the same journals in order to gain knowledge.
> Clinical trials are in the millions, and research grants are often 6 figures.
Maybe for Nature, but other journals have high open access fees and publish research from groups with lower budgets. You could very well find journals for which the open access fees are in the order of four, five months of salary of the main researcher, just for sending the article to reviewers and hosting the PDF in a website at zero marginal cost.