> Are developers supposed to pay to develop? ridiculous

No. Developers are supposed to pay to access the hard work of the technical writers and developers who maintain MDN. I don't understand why you think it's self-evident that this work should be free.

Here is a longer explanation by the person who created the precursor to MDN: https://www.quirksmode.org/blog/archives/2020/08/i_love_mdn_...

Here is the HN thread: https://news.ycombinator.com/item?id=24159244