This study explored the complex landscape of factors shaping students' engagement in online environments. The aim was to uncover hidden relationships and understand the roots of low engagement among university students. An interview based on the Decision-Making Trial and Evaluation Laboratory (DEMATEL) approach was used to model the factors contributing to students' online engagement. Prior to the interview, a systematic literature review was conducted to identify the influencing factors to form the foundation of the DEMATEL matrix for this study. By drawing insights from the perspectives of 50 students at different university levels, the study sought to understand how these factors might t mutually influence each other. The results revealed eight core factors consisted of online course activities, prior experience, course design, student-student interaction, course content, system interaction, university support, LMS structure and interface. Conversely, seven factors such as academic skills, instructor-student interaction, student-content interaction, active and collaborative learning, time on task, motivation, and feedback were found to play a secondary role in shaping students' online engagement. The study intricately maps and describes the causal relationships between these key and secondary factors, providing decision-makers with timely insights on how to mitigate students' low engagement with online learning environments. With this understanding, interventions can be tailored to elevate engagement in online courses effectively. The outcomes can also guide decision-makers towards identifying effective strategies for enhancing the online learning experience, contributing valuable perspectives to the discourse on improving student online engagement.