You invited the right person for this question! I'll tell you my story.
4 years ago I was living with with my parents in Naples, southern Italy, where people still think Java and Oracle DB is the new hot thing. (Meanwhile, in the north of Italy, I know for sure there are some companies using RoR - no more than 10 anyway).
I was doing a lot of C++, PHP, JS and (oh my gosh) some WordPress development.
One day, for no particular reason, I decided to learn Ruby on Rails. For my particular background I found Rails very steep to learn, yet incredibly satisfying. I had no plans at all, and back then I was still a University student.
When I felt confident enough I added "Ruby on Rails" on my LinkedIn profile and made sure that some friends upvoted that skill for me.
After ~6 months I get this email from a company in Naples looking for Rails developers. And I thought: you're kidding me, no way anyone is using Rails 500 miles from here.
So, what did happen? This company started with two Developers, and they were given freedom of choice for the language. They didn't know anything about RoR but decided to give it a try anyway. Fast forward 1 year, they left the company and moved abroad.
The company started desperately looking for other RoR developers in the area, and looks like I was the only person in a 400 km radius with the skill on LinkedIn. I got interviewed and hired. You cannot imagine the monsters I had to fight in that code, being developed from two people experimenting with the language while building it.
6 months ago I left that company. I now live in London and have been hired as "Senior Ruby Developer" whatever that means.
So, I may have been lucky, but being the only one practicing a skill in a geographic area can be a strong advantage!
Also, RoR is awesome.
Finally, RoR jobs are usually paid 10 to 20% more than other development jobs, mostly due to developer scarcity - and for the low time to market that Rails provides.