If by "capital product", you mean business, there's plenty. The most popular in these circles is: https://www.pragmaticengineer.com/

But it's not easy. I tried it for a TikTok content ideas, gave up after a few months: https://tiktokexamples.com/blog/shut-down-newsletter/

it never hurts to try something! good experience i hope, in the end. pragmatic is a great example. feed me, too. i was trying to think beyond substack. goop was the biggest one I could think of that turned to physical DTC. but all very interesting. the reason i was curious is the rise of actual brands making newsletters is seemingly less popular than organic newsletters that grow into brands or businesses.

Yep, it's simply due to specialization and survivorship bias.