Wordpress has:
* the ability to schedule posts
* a ton of plugins
* a lot of people who know how to use it
* a reasonable WYSIWYG interface
As far as I know, most SSGs fall down on one or more of those dimensions.
3rd bullet. I do a ton of WordPress at work. Clients asked for it because they know how to use it.
* live preview
3rd bullet. I do a ton of WordPress at work. Clients asked for it because they know how to use it.