Gatsby is an open-source static site generator that integrates React and GraphQL, offering a range of features that make it a compelling choice for web developers. The author highlights several reasons for switching to Gatsby, including its compatibility with React components, an extensive plugin system that enhances its functionality, and a unique data fetching layer using GraphQL, which allows for data integration from various sources. Gatsby optimizes performance with static HTML files for fast load times and offers Progressive Web App features to enhance user experience. Additionally, the developer experience is noted for being enjoyable, due to the ease of extending functionality through plugins, live-reload capabilities, and robust documentation.