But some pretty successful startups used it and some successful companies today use it. It's been a tool used to spawn quite a few billion+ dollar companies.
Ruby is a fine language that some people have ridden to great success. It is still a fairly niche language.
We're on a popular website written in Arc -- likely the only website written in Arc. Popularity isn't everything and I'm not suggesting it is.
Ruby developers is small in % but rather large as an absolute number.
Smt88 is correct in that it is increasingly a niche. Churn rate is greater than retention rate. Junior Developers cant find jobs with Ruby and Rails, and they switch to others that do find them jobs. Companies only want to hire experience Ruby Rails developers but some of them moved on. It is a vicious cycle.
The point is even if Reddit was written in Arc, it has no bearing on Arc's industry status. It needs to be in a self sustainable ecosystem.
The fact it's used internally at Google and MS alone means it's got traction. I'm willing to bet lots of enterprise shops are using it for things, even if it's not #1.
My own personal experience as a CTO and startup investor: I haven't seen Ruby (or even met someone whose primary language is Ruby) in a long time.
I think it had a moment ~10 years ago when a lot of people started companies using Rails. Some of them still use it, most of them just went out of business.
It hasn't been big since then. It seemed to only ever have become popular in a fairly limited bubble of startups, especially in Silicon Valley.