Which it is, actually!
Think about how MVC works in iOS, or ASP.NET MVC or JSP Model 2, etc. In the case of the latter two, your state is stored in the session as simple, regular objects. Have you felt the need for actions and reducers and immutability etc. when using session state? I have not.
When programming JavaScript SPA, you can program in the style of MVC also. There is no need for actions, reducers and so on, unless your app is for example a word processor and you need undo/redo (as mentioned by another comment on this thread.) Most of the time you are getting data from the backend, temporarily storing stuff in memory, modifying it and sending it back to the backend. There is no need for actions/reducers and such other nonsense for that.
When I mention this someone always points me to the "you may not need redux" article by the creator of redux, in an attempt to legitimize some use cases of redux. There may indeed be some legitimate uses cases for redux. But it has become the de facto standard way of building React applications, and that's totally unjustified.