You may not like it, but “arbitrary” isn’t a fair description; there’s reasoning behind it that is over 10 years old:

http://0pointer.net/blog/projects/stateless.html

https://www.freedesktop.org/wiki/Software/systemd/TheCaseFor...

That said, my knee-jerk is also that this is about strong-arming distros. Which leaves a bad taste in my mouth. I’d be interested to hear other viewpoints though.