Most state management libraries help you deal with the problem of sharing state between multiple components. In modern React, most components are just functions, so this boils down to passing state through deep call stacks.
If you have a component A, which renders component B, which in turn renders component C, without a state management library you'd have to pass state from A to B to C (this is often called prop drilling). The longer the call stack, the more irritating this becomes.
State management libraries allow component C and component A to modify, and subscribe to a shared state store. Redux et al. are effectively the reactive version of global variables.
React already has a mechanism for this (Context). It's not the primary reason to use a state management library.
Any discussion that doesn't revolve around a difference between the two is akin to suggesting re-implementing a standard library call for literally no reason.
The commenter I was replying to wasn't inquiring about why people choose third-party state management libraries in lieu of the standard context api. In fact, he's not even a web developer.
He seemed to be wondering why you need a state management solution in the first place. If he had asked why people prefer Zustand, or Redux, or Recoil over React's built in context api then I would have replied accordingly.
I was largely expounding upon the linked article's first list item under the heading "The problems global state management libraries need to solve". The first item in that list begins with:
> Ability to read stored state from anywhere in the component tree. This is the most basic function of a state management library. It allows developers to persist their state in memory, and avoid the issues prop drilling has at scale.
I would argue that the primary function of state management libraries is still sharing state between components. Third-party libraries might expose a more performant, simpler, or more intuitive api, but that's still their primary purpose. Analogously, if a non-compiler developer asked why programming languages need memory management, you wouldn't delve into the differences between reference counting and tracing garbage collection.
If you have a component A, which renders component B, which in turn renders component C, without a state management library you'd have to pass state from A to B to C (this is often called prop drilling). The longer the call stack, the more irritating this becomes.
State management libraries allow component C and component A to modify, and subscribe to a shared state store. Redux et al. are effectively the reactive version of global variables.