MOSFET heats during low pulse width in SMPS

[mitz]

https://www.falstad.com/circuit/#%24+1+5.0E-6+23.47059216675035+51+5.0+50%0Ar+160+272+80+272+0+10000.0%0At+160+272+208+272+0+1+0.5628227334851401+0.6412403660766932+100.0%0Ar+208+320+80+320+0+10000.0%0Aw+80+272+80+320+0%0Ag+208+432+208+480+0%0Ar+256+256+256+160+0+1000.0%0At+432+256+496+256+0+-1+-0.5949818600037027+-0.6146413135012256+100.0%0Aw+496+160+496+240+0%0Ar+304+256+384+256+0+10000.0%0Ar+304+352+384+352+0+10000.0%0At+432+352+496+352+0+1+-11.901922913629022+0.07841763287345535+100.0%0Aw+496+272+496+336+0%0Ag+496+448+496+480+0%0Ar+496+336+592+336+0+10.0%0Af+624+336+688+336+0+5.0%0Ar+624+416+688+416+0+4700.0%0Aw+688+352+688+416+1%0Aw+624+416+624+336+0%0Ag+688+416+688+480+0%0Aw+592+336+624+336+2%0Aw+208+256+256+256+2%0Aw+256+256+256+352+0%0Aw+208+288+208+320+0%0Aw+256+160+496+160+0%0Aw+496+160+576+160+0%0AR+576+160+576+80+0+0+40.0+12.0+0.0+0.0+0.5%0Aw+208+320+208+432+1%0Aw+496+368+496+448+1%0Aw+384+256+432+256+2%0Aw+384+352+432+352+2%0Aw+256+256+304+256+2%0Aw+304+352+256+352+2%0Al+576+160+688+160+0+4.9999999999999996E-5+0.48370700345111073%0Ad+576+288+576+160+1+0.805904783%0Ac+688+160+688+288+2+9.9E-4+1.136257487865672%0Aw+576+288+688+288+0%0AR+80+272+80+192+0+2+5000.0+5.0+0.0+0.0+0.5%0Aw+688+288+688+320+0%0Aw+688+288+768+288+2%0Aw+688+160+768+160+2%0Aw+768+160+832+160+0%0Aw+768+288+832+288+0%0Ax+885+230+938+236+2+24+Load%0Ar+832+160+832+288+0+10.0%0AThe load is a 12V, 2Amps DC motor. PWM Frequency is 62.5 KHz. Why does the MOSFET gets very hot during low pulse width?
The motor is started and stopped every 4 seconds.