TL;DR: Arch-OpenRC is deprecated; all work is now focused on
Because systemd is bad.
But, since you've clicked, have some longer ones:
The best example of suck
Systemd: The Biggest Fallacies
The End of Linux
Arrogance and crappy attitude
root shell exposed by failed systemd rescue mode
in Ubuntu 14.04.
systemd: a case study
Coming up next: package manager hooks for direct control by systemd