[Isinlor]

In many countries you could sponsor PhD student for a year on €9,500.

It's just crime in white gloves. Academics are defrauding public money by having anything to do with Nature.

Running Arxiv per paper costs somewhere in the order of 10 dollars.

[krab]

From the list of latest articles[1], you can see it's indeed not the most popular option. Only one in seven articles from the last few pages is OA.

The other OA journals still cost money that needs to be budgeted, i. e. not something you would pay out of your pocket. For example PLOS One charges you $ 1749. I guess the prices for publishing the articles may actually converge on a fair price for the reputation associated with the journal.

[1]: https://www.nature.com/nature/research-articles