The Newton is the SI unit of force. It is not in everyday use. There is no logical reason for not doing so. A force of 1 Newton on the balance pan is approximately the force exerted downwards by 100 grams of flour on the pan. The pompous answer is that using Newtons allows this diagram to be used on a distant planet with a different mass.
Weight is the expression of the force exerted by the earth on the mass of an object.
The mass is the fundamental quantity, the weight, even on earth, varies with the position of the object. 1 Newton of flour would work just like on earth.