Not despite, but because of!

Yhwh reveals Himself as a God of grace and mercy who is firmly committed to His covenant relationship with Israel. This understanding reaches a further climax in Moses’ final petition for the pardon of Israel’s sin (Exod 34:9); it is climactic because Moses makes Israel’s sinfulness the basis for his plea for divine forgiveness (“Forgive their iniquity because it is a stiffnecked people”). In other words, Moses, in an audacious yet profound way, makes Israel’s hopeless state the principal reason for his appeal to divine grace and forgiveness.—Standing in the Breach, page 510 (emphasis original)

<idle musing>
Wow! Did you catch that? Because of their stiffnecks, not despite their stiffnecks! That is ḥesed at its finest! Prevenient grace, the grace that goes before and awakens the sinner.
</idle musing>