I guess reading the history, systemd did a better job of dependency resolution and parallel loading of startup services. Then some less interesting stuff like logins, permissions, and device management - which definitely seems out of scope. There's been like 15 alternatives since it was made, but none of them got critical mass, and now pretty much every mainstream distro can't run without it. Sad face
While I'm here complaining, I really miss the days when Arch was configured from a single global file that handled many things like setting your hostname, locale, etc. I think it was dropped bc of maintenance & being not unixy enough. Kinda ironic