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.
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.