Building a new website used to be an incredibly expensive, confusing, and long process. Many non profit organizations in particular have avoided updating their sites due to worries about huge bills and complex decisions that they are unsure how to make.
WordPress is a heavenly piece of code. Where others feel the need to load their content management platform with features, WordPress gives you the bare minimum and lets the community dictate what kind of machine you can build with it through the use of plugins. One could make the comparison that WordPress is the Legos of the 21st century. This makes me want to sing "Everything is Awesome!".