The on-resistance of the Mosfet increases when it gets hot. That causes it to get hotter. That causes the on-resistance to increase more. Thermal runaway.
A low resistance Mosfet switching very quickly gets cooler as it pulses PWM at a lower average current. It gets hotter if it switches slowly. It has a high gate-source and feedback capacitance so it is difficult to switch quickly.
A low resistance Mosfet switching very quickly gets cooler as it pulses PWM at a lower average current. It gets hotter if it switches slowly. It has a high gate-source and feedback capacitance so it is difficult to switch quickly.