Ruby has been steadily going down as favorite language for years. I have absolutely no beef with Ruby, but GP is pretty clearly pointing out the disjunct between continuing to use a language with a dwindling userbase, and requiring that userbase to have professional experience. In its home country, GitLab is one of the few to use Ruby to begin with.

>I suggest you spend some time gaining actual Ruby experience

Which requires those people to get jobs. If they can't get jobs in the language, they can't get experience in the language. This is already an issue with the more popular languages which are converging to the same point.