I've seen this expressed many, many times, and it is something that I've honestly never quite understood. I started with React less than a year ago, and it wasn't until I added Redux to my stack that I began to feel perfectly comfortable with,
To me, the fact that actions dispatched in whatever component would cause the global state to be recomputed which then got handed to react to render it just a no-brainer. This truly makes data in React flow just one direction. The tooling around it -- Redux DevTools -- also made seeing my app in action and debugging it so incredibly clear.
Without it, for me initially it was a struggle about where exactly to store certain state, and passing props and callbacks up and down all over the place. It wasn't clean or easy to reason about at all.
As someone who had very limited experience in the framework, Redux felt like a tool which made the pit of success for me pretty darn large. I do know that even Dan himself has suggested that people not learn them in conjunction, but to me, the coupling of them is so perfect that React only became a joy to use WHEN I introduced it.