I suspect there are two problems: 1. only a minority of people can even see the value in such a thing and 2. one size does not fit all. Different minds work in different ways. Even after learning that this class of thingies existed I still develop my own because I’m always thinking of some feature I want to add or some way to rejigger the UI to make it more efficient for me.

It seems to me that if you’re in the market at all, you want to roll your own. It has to fit your own individual way of thinking. It’s a extension of one’s own mind.