Create React app is a very good example of that.
Even still, there's a high learning curve before you can build a proper application. That's because you need to learn about client-side routing, page layout, and so on. If you'd like to perform server-side rendering for faster page loads, things can become even more difficult. More Info »
So, we need something simple but customizable.
Think about how web apps are created with PHP. You create some files, write PHP code, then simply deploy it. We don't have to worry about routing much, and the app is rendered on the server by default.