In this study, we provide insight into the mechanism of retention degradation after endurance cycling of HfO₂-based ferroelectric field-effect transistors (FeFETs). Transfer characteristics of the FeFET are compared with the current-voltage response of the ferroelectric capacitors (FeCAP) for better understanding of the retention loss mechanism after cycling. Furthermore, a multiscale simulation by using the Ginestra^™ modeling platform is conducted and the results show that charge trapping stabilizes the polarization switching and improves the retention behavior. Retention after cycling experiments are shown as well as pathways to reduce this degradation mechanism.