Immersive technologies are assumed to have many benefits for learning due to their potential positive impact on optimizing learners' cognitive load and fostering intrinsic motivation. However, despite promising results, the findings regarding the actual impact on learning remain inconclusive, raising questions about the determinants of efficacy. To address these gaps, we conducted a PRISMA systematic review to investigate the contributions and limitations of Virtual Reality (VR) and Augmented Reality (AR) in learning, specifically by examining their effects on cognitive load and intrinsic motivations. Through the application of an analytical grid, we systematically classified the impact of VR/AR on the causal relationship between learning performance (i.e., objective learning improvement) and cognitive load or motivation, while respecting the fundamental assumptions of the main theories related to these factors. Analyzing 36 studies, the findings reveal that VR, often causing extraneous load, hinders learning, particularly among novices. In contrast, AR optimizes cognitive load, proving beneficial for novice learners but demonstrating less effectiveness for intermediate learners. The effects on intrinsic motivation remain inconclusive, likely due to variations in measurement methods. The review underscores the need for detailed, sophisticated evaluations and comprehensive frameworks that consider both cognitive load and intrinsic motivation to improve understanding of the impact of immersive technologies on learning.