Why blender are not allowed to run for three minutes continuously?

Temperature issues I'm guessing. Besides I wonder if there's anything that won't blend in under 3 minutes!!

Actually all the blenders are having motor inside the body which rotates the blender blade.When we power-up or start the blender its motor runs and generate heat.It is the only body from which heat dissipate to out side atmosphere. Hence you feel heated body.Normally we can run the blender for 3 minutes or more depending upon the load (i,e if you are blending hard material;motor does more effort to rotate to blend) If you are in not hurry to blend just give some time to cool down the body temp to increase the life of motor (hence blender).