Why Struts2

"Apache Struts 2 is an elegant, extensible framework for creating enterprise-ready Java web applications. The framework is designed to streamline the full development cycle, from building, to deploying, to maintaining applications over time." - From struts.apache.org

Further from the struts2 site: http://struts.apache.org/2.2.1/docs/can-you-suggest-an-elevator-pitch.html

Personally what I like about the Struts2 framework is that it has set out to be the best Action based framework.  It is not part of a larger philosophy, it just went out to do that one task as such I find it simple and elegant.