Why does merely saying “death is merciless” not necessarily reproduce the claws-of-death construction?

Implicit and Imaginative Metaphor: Definitions, Core Examples, and Analysis

• It predicates a quality but lacks a distinctive animal attribute
• It openly names the source and thus is an explicit metaphor
• It contains a simile particle and is an overt simile
• It lacks a clear source-specific attribute invoking an unstated physical image