Maybe it's complicated, but perhaps it's trying to replicate daemon(3) without bugs, and for different processes. See the BUGS section in the daemon(3) man page.
> Given that it’s typed once (by the daemon author, and not the end user), it seems like a big win vs. daemon(1) to me.
This seems like a false comparison. It's not the case that the end user writes the code to daemonise in the non-included case. The user would just use daemon(1) or systemd(8) or something else that can daemonise. Or perhaps a service manager that doesn't need to daemonise, like runit(8) (https://smarden.org/runit/) and its ilk.
The more I read about this, the more I want to know why it's so important that pipewire is running "daemonized" (whether it does it itself or not). Can you explain the advantages and disadvantages?
Also, it’s incredibly complicated. (I looked at the source.)
Here’s a writeup of a simple daemon: https://pavaka.github.io/simple-linux-daemon-tutorial/
Given that it’s typed once (by the daemon author, and not the end user), it seems like a big win vs. daemon(1) to me.