PulseAudio is still a massive mess. It solved a tiny subset of surface level problems, eventually, and introduced a whole crap load of other ones in the process.
PulseAudio has been around, what, 10 years now, give or take? I think I've only stopped having to fight with it in the last couple of years. When it first landed it was by no means an improvement from OSS, and it took a while until it could realistically compete. It brought a bunch of advantages with it, but it was far from easy.
If you want to see a fun example of how annoying PulseAudio can still be, try and make a linux machine act as a bluetooth audio receiver. It takes only a couple of minutes work installing and configuring the bluetooth side of things. The PulseAudio side of things will suck up hours of your time trying to persuade it to be consistent, running through a godawful series of inconsistent command lines.
It's pretty clear that systemd is determined to unfuck the linux desktop experience. They're not solving problems that exist on the server side. When you look at the justifications for various bits of really breaking stuff, it's almost always (as in this case) coming down to something related to the desktop experience. They've futzed about with stuff, breaking things along the way, because it "speeds up boot." How often do you reboot your servers, and does it really matter that it's 20 seconds quicker?
The goal is admirable (The linux desktop can be a crappy experience, I've been using it as my primary work environment for pushing on 10 years now, and using it in general for closer to 15.) The methodology is not, nor is the attitude of the developers. They continue to approach problems from the perspective of "we know best", "not invented here" and "The only fix is a ground up re-write". Along the way they're making the exact same mistakes existing stable and mature software made decades ago. Worse, they're breaking things that really shouldn't be broken and they're betraying a complete lack of understanding about how linux is run in production environments. This particular case is a perfect example. They've decided that processes should be reaped on all systems, in all environments, when users log off. Not because this was a particular problem anywhere, but because some processes weren't being cleanly stopped when someone logged out of Gnome. It's fixing a minor desktop issue, something that doesn't affect the large majority of the user base, in a fashion that breaks what a large majority of the people actually do.
Here's another classic example: http://www.spinics.net/lists/netdev/msg365477.html systemd developers decided that the way IPv6 route advertisement was processed in the kernel was wrong (despite having been fully functional and stable for a long, long time), and decided that they really should do it themselves in an incorrect fashion.
At its core, the *nix environments core strength has always been that it's composable, focusing on complect over complex behaviour, creating a cohesive whole out of individual and specialised components that have specific tasks. You take a similar when writing software applications. Just as with writing software and using libraries, you use the ones that meet your requirements the best.
This flexibility allows people to build platforms and infrastructure that does what they need, and allows people to solve issues developers couldn't have anticipated in the first place.
Systemd's approach is instead a highly opinionated and inflexible "this is the way things will be". It's likely a perfect approach for a desktop environment, but that's not where it's being restricted to. The primary consuming environment is servers where they're 'fixing' things that weren't broken there in the first place.
To them systemd is golden, as you can see with how CoreOS is basically built around systemd.