Why would a vassal prefer to pay the scutage over levying men?

Levying men is expensive – you have to pay for the arms and armor, the horses, the food, everything – and it’s risky too, because unless you get plunder or rewards from the king you’re not going to get anything for your service, and if you lose you could die or have to pay a hefty ransom. Moreover, levying men meant spending a good deal of time away from your estates – a lot of time if the war was far away, as was the case during the Crusades, for example.