Supposedly network transparency came later.

Best i could find, Poettering started work on Pulseaudio because he picked up a usb headset (basically a usb soundcard with tethered headset) and ran into issues with switching the IO streams around mid-use (say plugging it in while in the middle of a Skype call).

Not sure why he passed on using JACK though, or if it was not mature enough for him at that stage.

Also, i don't think Alsa had dmix (user-space software mixing) at that point in time.

As best i can find the one thing Alsa is missing is a interface other than .alsarc for configuring pr user virtual devices.