Before JSF was developed, Java web applications were typically developed using non-standard web application frameworks such as Apache Struts, Tapestry, Spring Web MVC, or many others. These frameworks are built on top of the Servlet and JSP standards, and automate a lot of functionality that needs to be manually coded when using these APIs directly.
Having a wide variety of web application frameworks available (at the time of writing, Wikipedia lists 35 Java web application frameworks, and this list is far from extensive!), often resulted in "analysis paralysis", that is, developers often spend an inordinate amount of time evaluating frameworks for their applications.
The introduction of JSF to the Java EE 5 specification resulted in having a standard web application framework available in any Java EE 5 compliant application server.