My personal theory on why rails never beat out Wordpress (beyond that it has different goals), is that any attempts to make a Wordpress competitor never addressed end-user plugins.

Ruby has package management called Gems. And while these are easy and powerful for a programmer to call on; they aren’t loaded using a visual interface and be able to be dynamically loaded by the end user as is the experience with Wordpress.

To make a real Wordpress competitor; a system of user-self-installable plugins needs to also be created. Now that’s harder than just making a CMS but it’s fuctionality that makes many so called Wordpress competitors non-starters.