Why does it matter?
Anyone can make their own distro, most are just a software bundle and very little if any development is put into it.
The waste majority of Linux users are using the main distributions, and by fare the most development time goes into shared projects like the kernel, GNOME, kde, etc. If you look at all the work that is done, and how much that directly or indirectly ends up in the top 10 Linux distributions, it’s probably +90%. Very little work out of the total amount goes into the one-man projects.
Linux has always allowed people to explore their own solutions, and the community decides if their solution is worth adopting. If you removed all the one-man projects, it wouldn’t mean that the same people would start working on one of the main projects, for many it’s just a hobby project they work on in their free time.