“So you have a filter with many layers: you need areas which fulfill a stringent set of conditions for such an educational newsletter, and you need a very unusual sort of individual, someone who is expert in the area and has preferably gotten their hands dirty, who is good enough to work professionally in it, but who also is capable of explaining it well, at a beginner level, many times, endlessly without burning out or getting bored, because of their intense interest in the area (but again, not quite intense enough to make them go do it instead of write about it).”

I think the first filter is a much bigger factor, but for a reason that’s not mentioned in the post: $$$s to be gained. A large number of people read finance blogs because they think they themselves make money with the knowledge therein.

This is hard to replicate with other examples given: for purely abstract topics, eg Greco-Roman philosophy, the prize is purely intellectual. For others, eg fracking and drug discovery, you can make tons of money but pool of interested people is much smaller.

The only combination of general appeal and personal gain that could be interesting, I think, would be dating. You have recurrent patterns, clear outcomes, and pretty much everyone is interested and want to learn how to get better at it.