Why is the word 'zero' not used a code word for the letter 'z' in the NATO alphabet?

Why is the word 'zero' not used a code word for the letter 'z' in the NATO alphabet? (*) Because it can be confused with the number '0'. (*) Because the word 'Zulu' is easier to pronounce. (*) Because the word 'zero' is not well known worldwide. (*) Because 'zero' sounds too Italian