Hiring a JSTL developer is beneficial due to their expertise in JavaServer Pages Standard Tag Library, a crucial technology in Java web development. They can create dynamic web pages with custom tag libraries, enhancing the readability and maintenance of your code. They bring efficiency in code reusability, reducing development time and cost. Their skills can help in creating flexible, scalable, and interactive websites. Additionally, their knowledge in JSTL enables them to handle XML documents, internationalization, SQL statements, and more, providing a comprehensive solution for your web development needs.