The zipper is a component. If the component works as functioned, there's little reason why you would risk trying someone new.
For new companies to figure how to perfect the component takes time. They could probably try to innovate the zipper but that depends on whether designers would be willing to pick up on it. Even then, it would probably cost a lot of money to set the process up and mass produce those new, untested zippers. The risk/reward is just not favourable to an investor.
For competitors, producing the perfect zipper is one thing but maintaining supply whenever is needed is another issue. Your logistics have to be in place. And then there's also the relationship. Reliability counts when it comes to being a supplier.
For new companies to figure how to perfect the component takes time. They could probably try to innovate the zipper but that depends on whether designers would be willing to pick up on it. Even then, it would probably cost a lot of money to set the process up and mass produce those new, untested zippers. The risk/reward is just not favourable to an investor.
For competitors, producing the perfect zipper is one thing but maintaining supply whenever is needed is another issue. Your logistics have to be in place. And then there's also the relationship. Reliability counts when it comes to being a supplier.