Final answer:
Most zippers have YKK because it is the name of a famous zipper manufacturer known for its high-quality zippers.
Step-by-step explanation:
Most zippers have YKK because it is the name of a famous zipper manufacturer. YKK stands for Yoshida Kogyo Kabushikikaisha, which is a Japanese company that has been producing zippers since 1934. YKK is known for its high-quality zippers and has become the industry standard.