This is what Ruby on Rails has. People are selecting Rails, and it just happens to be written in Ruby. This seems weird, because it's a developer framework and intimately tied to the language, but it's clearly what's happening.
It is weird, especially with all the comments along the lines of "I use Rails even though I don't really like Ruby". I can't understand not liking Ruby, but I do enjoy reading these comments.
But it's easily explained: Rails lets you create applications using absurdly little code, so the barrier to entry is low. Low enough that it's worth trying, even if you're unsure about the language it forces you to use.
And actually there are several competing web frameworks in the Ruby world. Rails didn't first take over the Ruby world, then expand to the wider world -- instead it immediately went to the wider world, and has been consolidating the Ruby world more as an afterthought.
A few people have doubted that it will consolidate the Ruby world, because some/many Rails newbies seem to totally understand that Ruby is a very powerful general-purpose 12+ year old programming language, not merely the Rails scripting language. That may be a PHP background, where the language is the web development environment (or something).
I disagree with that opinion, because you can't do much in Rails without programming some Ruby, and if your app does anything remotely interesting, you're going to have to learn how to manipulate data, etc. So education will have to take place somewhere. However, if you weren't attracted to Ruby for the langauge itself, it's not certain you'll strengthen its community. It's already clear that the Ruby and Rails communities are distinct, though very much overlapping. That's good, because the two communities serve different purposes.