Why doesn't the pliers wrench close completely in parallel?

If you look at the closed jaws in the unloaded state, a light gap is visible in the rear gripping area of the pliers wrench. This “slot” guarantees that the jaws will lie completely parallel to the gripped workpiece under load (under load, the components always bounce a little bit).

Pliers wrench

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Pliers wrench
Pliers and a wrench in one tool