The problem is that the surface of Angular is incredibly complex.
With React, you have components, which are just things (classes or functions) that convert a set of properties to a subtree of more components (ideally mostly ones that directly represent DOM elements) and do so deterministically and reproducibly.
With Redux you just have objects ("actions") representing changes to your application state and functions ("reducers") that convert an action and the current state into the future state. There are also functions ("action creators") that help you create the former and functions ("middleware") that affect how Redux processes them.
With Angular1 you have templates and directives and components and models and scopes and controllers and filters and injectors and services. And services can be constructors or factories or providers or values or constants or decorators. And scopes can be isolate or nested and there is the digest cycle and there are watch functions and if you do anything async outside of Angular you need to make sure to trigger the digest cycle (but not if you're already in the digest cycle) and I haven't even talked about interpolation yet.
Angular2 is slightly better but the docs are pretty sparse and many people's brains will still shut off as soon as they hear "dependency injection" and have you fucking seen what they have done to HTML to maintain their false illusion of "it's just HTML and JavaScript, designers can understand this"?
React doesn't need you to think. Initially the API made you define components by using a magical function, then they extended it to allow just using ES2015 classes, now you can even define simple components as plain old functions. The surface has shifted from minimal to nearly non-existent.
Redux has more conceptual overhead than React ("Wait, reducers can't have side-effects? Where does my AJAX go?") but most of the learning time is spent un-learning concepts you take for granted (e.g. you shouldn't mutate state, your components should ideally not have any state at all and it's perfectly fine to normalize your state because you only need to derive it when it actually changes). The number of actual concepts Redux brings to the table is fairly low.
Angular is a battleship. React+Redux is an attack submarine.