Why was Bootstrap Bill's blood necessary to break the curse? Essentially, the curse is only lifted when every single Aztec gold coin is returned to where it was taken from, along with a penance of blood from all of the men involved in taking it. And this makes sense, at first sight.

What is the Aztec curse?

The curse of the Aztec Gold, also known as the Aztec curse, was dark magic cast upon the treasure of Cortés, consisting of a stone chest with 882 pieces of Aztec gold.

Why is Jack Sparrow not cursed?

The ousted Captain Jack Sparrow wasn't party to the theft, so he isn't cursed by it until he tactically allows himself to be in his final fight with Hector Barbossa. However, Jack's history with the Pearl exposed him to a different supernatural danger.