Hi, everyone:
I don't think popularity has waned much, if at all. For awhile there was a lot of buzz about Ruby and how it was going to topple the giants - Java, Python, C#. But that never happened, and when people look back on, say, 2010, and compare it to now, they don't see the same level of excitement or hopefulness. That's understandable, but doesn't necessarily reflect a decrease in usage or, certainly, utility.
I view the history a little differently. I love Ruby (obviously), and I think the language maintaining its status as an underdog gives it distinct advantages. It doesn't have to support every release ever made (Java) or lock itself into only one right way of doing things (Python). It's free to experiment, take suggestions and contributions from an active community, and cultivate it's already strong following. In programming, as in life, the most popular things are not always the best!