Take that small scale subsistence farmer. Individually, they will live a precarious life. Their country will not have the surplus food needed for other pursuits like building cities, engaging in R&D, developing science, and so on. A smaller and smaller number of people need to be able to feed more and more using less land per person.

Manually copied manuscripts are another example. They were painstakingly copied over by hand in an incredibly low productivity manner. The introduction of the printing press essentially eliminated an art form, but gave rise to practical mass media.

In the present day, computers have been the main form of productivity booster. While arguably social media is a drag on productivity, overall computers open up a broad range of possibilities.

Like yo, cancer is incredibly productive.

Cancer is incredibly costly to society. Think about it, a single person getting cancer could mean many hours of them being in the hospital. Net zero on productivity

Demolishing subsistence farms and replacing them with cash crop slave plantations is mad profitable.

As I detailed above, transitioning from unproductive farms to highly productive farms is necessary. Don't believe me, ask Mao.

I could make thousands of dollars in a day if I just sold everything I own.

That would not be a productive activity since there would be no value added. Arguably there would be less value, since that stuff is likely worth more to you than it is to another person.