They made the only choice. Because various applications are now dependent on systemd APIs in order to function correctly, and those APIs in turn can only be implemented by an init system that is structured the same way as systemd, it's essentially impossible to use anything else. Someone could come up with an alternative to systemd that was superior in every other way and it'd be impossible to move to it. (Hell, it'd have been impossible to move to systemd in the first place if the existing init system was so closely entwined with everything else.)
