There were a bunch. Radiant CMS, Refinery, Locomotive, and others.

Three problems (1) PHP is deployed all over cheap shared hosting providers (2) no one who uses a CMS cares about the backend (3) Wordpress has massive ecosystem

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.