I think the hype around Groovy was at its peak when folks were the most interested in having something like Ruby running on the JVM, and jRuby did not yet seem like a viable option. But even the hype for classic MRI Ruby has been waning, as developers look to do more with concurrency, and they discover dynamic everything-is-mutable languages have limits when it comes to concurrency. See Tony Arcieri's article "2012: The Year Rubyists Learned to Stop Worrying and Love Threads (or: What Multithreaded Ruby Needs to Be Successful)" and where he wrote:

"I’m talking about at Dr. Nic’s talk at RubyConf 2011, a little more than a year ago. Dr. Nic had a fairly simple message: when performance matters, build multithreaded programs on JRuby (also: stop using EventMachine). Now granted he was working the company that was subsidizing JRuby development at the time, but I didn’t, and I for one strongly agreed with him. Not many other people in the room did. The talk seemed to be met with a lot of incredulity."

So even among Rubyists, there has been growing interest in Ruby beyond the MRI, and if that is happening in the land of Ruby, then the argument for Groovy is that much weaker.

At the same time, the growing interest in dealing with concurrency certainly helped increase interest in Scala and Clojure, and furthermore, functional programming in general. If you are a developer who wants to harness the power of concurrency for greater speed, Scala and (especially) Clojure are full of interesting ideas for how to do that. Groovy, meanwhile, feels off-topic.