Prior to all of the important distributions consolidating on systemd, you had to support each distribution’s convention for customization, overrides, dependencies, conventions for things like changing users or locations for PID files, not to mention the differences in various shell tools.

Nothing insurmountable but it meant init files were inevitably much longer than the corresponding Upstart or systemd files despite doing less, and anytime we shipped a new version you had more testing since you had to implement a lot of functionality which is built in to other things.