Relying on a single factory, or a single country, for a full product line feels efficient right up until it isn't — a port closure, a labor dispute, or a single failed inspection can halt an entire season's inventory overnight.
Brands that diversify across two or three qualified factories per product category rarely pay much of a cost premium for it, and in return gain real negotiating leverage and the ability to shift volume quickly if one partner underperforms. The upfront work of qualifying multiple suppliers pays for itself the first time something goes wrong with one of them.