I'm not the creator of this, but to me React isn't about speed, it's about creating isolated, testable components within an understandable architecture. Given that, it's just as useful here as it would be anywhere else.

As oppose to plain Javascript? Or why is it in the title?

The former can be asked of any library / framework. Visit React's website to learn about why it's useful. Others have covered some reasons: it makes reasoning about applications easier and makes falling into composition of (mostly) stateless components the default

The latter is because people might be interested in seeing what's possible in React. Even viewing the page in React's dev tools is interesting and shows the author is also using Redux.

Helped it get to the front page!

Seriously though, React and Typescript are both technologies some people prefer to work with, because they find it easier to be expressive/reason about their application's architecture. The 'point' usually boils down to that as far as I know.

The point is click baiting, this is mostly a web audio and canvas driven app.