And for that "simplicity" all you need is a daemon that depends on dbus, glibc and cgroups (IIRC), just to name a few - which makes it non-portable for anything that isn't Linux and non-usable for anything that doesn't want to depend on, say, glibc.
And if they got their way, dbus would have been shoved into the kernel (kdbus, bus1, or whatever they called it) - adding a bloated mess of an IPC mechanism into the kernel.
Simplicity. Right.