Having a monopoly is not necessarily a death sentence for your firm.
Ykk basically has a monopoly and they're fine. You can tell they're fine because you've never really thought about your zipper before. They just work. When zippers have issues it's because Americans are cheapskates, not because Ykk can't make a good zipper.
I would be interested in investigating what they do differently.
I accidentally investigated a bit just now. They're not a public company. That's 100% relevant. Incorporated and joint-stock, but not publicly traded. Don't have to make the Dow Jones happy. Result: this is the first time I've seen a corporate wiki page that has both revenue and profits with the green triangle. Not coincidentally the latest data is 8 years old - uh, actually, how much money they make is none of your business. They make enough. Just buy your zipper and piss off.