Most of these categories are niches that the average person has some experience with and don't require specialized knowledge or connections to create a successf

Most of these categories are niches that the average person has some experience with and don't require specialized knowledge or connections to create a successful product. Most programmers don't know enough about non-programming fields to build a successful product, so they all tend to pile on in the few niches they understand. There are probably a lot of business opportunities out there for programmers who also have experience in non-software fields.