I have had exactly the opposite experience. I recently rolled onto a React project without Redux and the code was pretty gross. Multi hundred line React components with markup, API calls, and business logic all mixed together in an untested and untestable cocktail garnished with a heavy dose of prop drilling and deeply nested callbacks.

Adding Redux to this app was a huge improvement. Test coverage is now almost 100%. The views are now tiny and simply render props and dispatch actions. Complex workflows are handled beautifully by Redux sagas. Overall, the codebase is now one of the cleanest I have ever worked on.

I am not saying you have to have Redux to have a good frontend codebase, but it definetly helps a lot. If your app is even remotely complex, its hugley helpful to have a global data store. If you are going to have workflows with asynchronous components, Redux sagas are an incredible tool.

My hunch is that the apps that don't use Redux either 1. suck or 2. have had some smart person hand roll a framework that has most of the core principles of Redux in it. I am not that smart, and I don't want my codebase to suck, so Redux is the best choice for me.