I feel like the people complaining about how many libraries there are in this stack don't know what these tools do. Most are small tools that do one thing very well. Yarn installs packages, much like Gem, NuGet, whatever. Pretty standard. React is a frontend framework. Not surprising that you'd use one. I suppose you could opt to write a giant pile of vanilla JavaScript instead (I'm assuming you're not using this kit…
The problem that most of us dislike the javascript/web ecosystem is that those set of libraries and tools keep changing every couple years. As someone who doesn't do this as a full time job but once in a while has to poke his head out to the other side, it's really hard to keep up with even the acronyms. For example, I know that we are using npm, but now you say we should use yarn?!