My guess is that if PulseAudio had came later, it would be called "systemd-audio" or something like that.
If it dynamically creates systemd units or sets their properties (systemd-homed, systemd-networkd, systemd-resolved) using the dbus endpoints, it's systemd-something.
If it uses systemd libraries and lives in the systemd repo because it shares baseline docde, it's systemd-something.
systemd is modular in the sense that those components are build-time flags. For homed, for example: https://github.com/systemd/systemd/blob/main/meson_options.t...
Again, not confusing. Literally looking at the systemd repo for longer than 30 seconds would show you both why this it's considered modular, and why it's systemd-whatever
Pulse doesn't.
It is because systemd confuses what should be split concepts into one big overarching thing.
'org.freedesktop.systemd1' (the actual systemd init D-Bus interface) somehow is still implied that it is vital to the entire systemd-something ecosystem while it's not really.
A example being systemd-hostnamed and hostnamectl complaining that 'System has not been booted with systemd as init system (PID 1). Can't operate.' [1] while in fact they use 'org.freedesktop.hostname1.${something}' [2] and that is supposed to not be bolted with the entire rest of systemd besides using sd_bus.
[1] https://github.com/systemd/systemd/blob/93258c7d72fae23c9f81... [2] https://github.com/systemd/systemd/blob/93258c7d72fae23c9f81...
