Not necessarily. You can build a perfectly good website using HTML, CSS and vanilla JS. That said, React does make some things easier, such as structuring your code and aiding code reusability. Many of the benefits React brings only really come into play if you're building something at least a bit more complex than a simple site. There are several reasons why lots of companies and individuals prefer using React, but equally, vanilla JS might be exactly what you need and React might be overkill & not worth the learning curve if all you want is a simple site.