A lot of people are afraid of systemd expanding because systemd handles a lot of stuff, so distros are likely to support it rather than the mishmash of tools they personally prefer. It all started with the System-V/Upstart replacement and now very few distros have the patience to customise and roll out the 90s style service management anymore. Their preferences used to align with the mainstream, but no longer do these days, and that causes friction.

This process pushes people who prefer old tools to fringe distros, and newer software is less likely to work on their setups. They’re still free to use whatever system they like, of course, but the burden for developing and maintaining daemon management scripts is now on their fringe distro or themselves if their distro doesn’t have anything yet. I’d find that pretty annoying too, especially with how convoluted many older system management scripts are and how many moving parts are typically involved. Plus, some stuff like socket activation can’t even be done with some of the older init systems so people have to find alternatives.

I doubt anyone reeling against run0 was ever going to consider it anyway.