Because it's trivial to mix-and-match specialized products in a single project. It's trivial to install docusaurus, and a ssg like eleventy in the same project,

Because it's trivial to mix-and-match specialized products in a single project. It's trivial to install docusaurus, and a ssg like eleventy in the same project, and configure it so that they have some shared components by setting configuration details to point to the right directory, all within one repo, same package manager, etc.