Working with the DOM API is hard. React basically gives developers the ability to work with a virtual browser that is more friendly than the real browser. React’s virtual browser acts like an agent between the developer and the real browser.
React enables developers to declaratively describe their User Interfaces and model the state of those interfaces. This means instead of coming up with steps to describe transactions on interfaces, developers just describe the interfaces in terms of a final state (like a function). When transactions happen to that state, React takes care of updating the User Interfaces based on that.
React is just JavaScript, there is a very small API to learn, just a few functions and how to use them. After that, your JavaScript skills are what make you a better React developer. There are no barriers to entry. A JavaScript developer can become a productive React developer in a few hours.