Inexplicably? They didn't want to fight against upstream. You'd have to maintain your own scripts for every daemon you supported if you didn't use systemd. Also

Inexplicably? They didn't want to fight against upstream. You'd have to maintain your own scripts for every daemon you supported if you didn't use systemd. Also other software like udev is getting sucked into systemd as well. Arch is a small distro and doesn't have the development power to customize everything.