The increasing demand for precision, productivity, and safety in construction has accelerated adoption of robotics and AI in steel building components prefabrication. This systematic review synthesizes 125 peer-reviewed studies to evaluate the state of robotics, AI, and digital technologies, specifically BIM, DfMA, and digital twins, across design, manufacturing, and assembly workflows for steel prefabrication. Using a novel five-dimensional Scope-Mode-Advantage-Restriction-Transition (SMART) analytical framework, the review characterizes major research themes, technological distribution, and associated performance outcomes. It highlights domination of robotic welding, additive manufacturing, and vision-guided inspection, but limited multi-robot deployment and integration with digital technologies. The review identifies critical methodological and operational limitations in the state-of-the-art and formulates a comprehensive roadmap for advancing steel prefabrication through five sequential research thrusts. Future opportunities include unified BIM-to-fabrication data pipelines, generalizable AI models for adaptive process control, scalable multi-robot platforms, and integrated real-time digital twin workflows to enable an intelligent robotic steel prefabrication ecosystem.