systemd is very much a cathedral. If two competing tools are implemented in both systemd and some independent project, you can bet that the systemd tool will appear in every single distribution while the competing tool will struggle to get through packaging acceptance even if it's by some reputable developer or project.

Shipping everything in a monolithic archive, even where it makes very little sense, is very powerful leverage. Suddently it's harder to exclude tools than it is to include them.