Interband Cascade Lasers (ICL) have matured into a versatile technological platform in the mid-infrared spectral domain. To broaden their applicability even further, ongoing research pursues the emission of ultrashort pulses. The most promising approach is passive mode-locking with a fast saturable absorber. However, despite vast attempts no passive mode-locked ICL has been demonstrated up to date. In this study we perform pump-probe measurements on the ICL gain and show that its dynamics are mainly ($\sim$70%) governed by a fast recovery time of 2 ps. Our findings explain why passive mode-locking has not succeeded so far, shedding a new light on ICL dynamics as we propose strategies to overcome the current limitations.
