Redux is an opinionated implementation of Flux architecture. The reason Facebook came up with Flux architecture is described pretty thoroughly in this video. It mostly had to do with front end scalability — the never-ending addition of components that required a single source of truth and simultaneous updating.
This is an important concept for developing scalable front end applications, but it causes more problems than it solves in small applications, which is the point of this article. Developers often opt for no global state as opposed to using Redux. When dealing with small applications, one-off applications not meant to be maintained or iterated over the long-term, or proof of concepts, then Flux architecture isn’t really solving anything.
When you get to FAANG-scale front end applications, you’ll probably want Redux or some other in-house variant of Flux architecture. However, even there, I know a lot of FAANG apps still avoid Redux in favor of simplicity.