OK. I am not a mechanical engineer or much of a mathematician... try a limiting case where the blades are ground perfectly flat, the edge bevelled appropriately and the blades curved slightly such that the cutting point travels outward from the pivot as the handles are closed.
Contact between the blades is the full width such that any debris prevents the cutting edges actually meeting. You can cheat by twisting the blades slightly to give a clearance. This leads to wear and an adverse bevel inside the blades which you cannot easily sharpen out.
Quite often someone else has used them for cutting grass laden with abrasive soil:-(