We use zippers when we have no other choices because zippers are famously unreliable. What is not unreliable is velcro; and nobody wants to have a wardrobe malfunction right before or during trooping ( hence velcro on the pants )
Sometimes we do not have a choice and zippers are a must. We will buy batches of zippers and when they arrive we test each a few times before installing and again after. While it is neither definite nor perfect, it reduces by 95% the risk of a bad zipper.
Alas, it may happen that a zipper “breaks” – not just in our products but in ALL products with zippers. There are easy ways to DIY a fix; and here are our favorite links about common zipper issues
alternatively you can also seek the help of a “professional”, a cobbler, a seamstress, dry cleaner…
The point is, a zipper does not necessarily need to be replaced and can be fixed easily and at low cost if you know what to do.