Because if you are beyond the notch, you are ignoring the preset values set for climb or cruise power. You put the levers in the notch and accept the power you get - that is what the engine manufacturer and atr have worked everything out on.
To move levers beyond notch to ramp is for Go Around and beyond emergency!
If you don't have the levers in the notch you are making the a/c ignore the pwr mgt switch. That is why you must bring it back to the notch after a Go around, even when on one engine, otherwise yes, you will burn out the engines!