The problem is there are better things before systemd, namely daemontools (and its derivs runit, s6, ...). It wasn't popular, presumably because people didn't care that much.
OTOH, Nosh offers a tool to auto-convert service files into equivalent daemontools shell scripts: http://homepage.ntlworld.com./jonathan.deboynepollard/Softwa...
Few seems to care enough either.
History of modern init FYI: http://blog.darknedgy.net/technology/2015/09/05/0/