As someone who was Elixir hire #1 at a company that eventually ended up with ~25 Elixir developers with a novel product that people actually used, I see people in this thread and elsewhere mentioning the unorthodox nature of the language or the supposedly poor performance, and I can tell you that none of that actually matters one way or another. The stuff that really hampers Elixir/Erlang adoption, in my own personal experience and from talking to friends who could have used it but went with other stuff:

1. From the outside, the benefits appear almost entirely theoretical, and in many cases, they are, and the issue with that is that in order to understand the real, non-theoretical benefits of having everything integrated into Elixir and OTP, you have to go all-in. Elixir has to own your app. Elixir is amazing, but when you start talking about its ability to do async IO, people say, "my language has a framework for async IO". When you start talking about its ability to automatically timeout and restart tasks and be fault tolerant, people say, "my language has a framework for network timeouts and I have systemd/k8s/whatever for application restarts". When you start talking about having ETS tables built in, people go, "I have Redis and it works amazingly well, why do I need it inside my app?" You can't adopt OTP piecemeal like you can with e.g., Tokio, or Redis, or Sidekiq, or whatever other thing. It doesn't really make sense to. Other languages might not be as powerful and not as well integrated, but through sheer force of effort, people make existing languages compose with general purpose tools and this is often "good enough". Of course you can write a single small service in Elixir, and this is fine and works, but this often runs into the issue of "now we have an Nth language beyond our normal languages, and we already have caching/monitoring/supervision figured out, so what is this actually adding?"

2. The library ecosystem is still very weak if you're used to e.g. Ruby, Python, Java, or Go (or even Rust, which already has way broader library coverage that is often significantly higher quality) and being able to find a mature driver/integration for a given API or native library. I don't know if this will ever catch up or reach a critical level where most people will find it acceptable. Stuff like the AWS library languished for, literally, years. Just critical stuff that's totally sorted in other ecosystems. This is purely anecdotal on my part, but it seems that way less people as a percentage of the whole community are working on libraries than applications. I have no idea why this is.

3. The performance - especially around latency and garbage collection - is great, but it's probably not "better enough" to actually matter in the domains where people tend to adopt Elixir. What I mean by this is, if you're already working on a project where the performance profile of Ruby or Python or Java is fine (web stuff, relatively simple network or CLI stuff), Elixir may be better in certain respects, but it's not so much better that it provides enough of a step change to make the other issues worth it. For our application, we had some very CPU intensive math stuff that dominated processing times, but we wrote that in Rust anyway, so the higher-level control layer could have been literally anything and it wouldn't have had any effect on performance at all. We picked Elixir because we liked it, but the product would not have failed for performance reasons if we had picked Ruby.

4. It is still, somehow, relatively difficult to find Elixir developers that understand OTP and the more operational concepts of the ecosystem (releases, deployments, observability etc.) at more than a beginner level. The community is still rather beginner oriented and there are a ton of folks who have done simple Phoenix apps and never gone further. I want to be clear that I mean this simply as an observation and not in a derogatory way at all. There is absolutely nothing wrong with having beginners in your community. Beginners are essential to ensure the community continues to grow and a language community without beginners is dying. But over time you have to build up a significant base of experts that can start and lead teams and companies independently, without having to rely on a class of consultants (of which the Elixir community seems dominated by - which is another conversation entirely that I will not get in to here). In Elixir, it seems like the proportion of experts has stayed small relative to the number of experts in e.g. Python, Ruby, Clojure, Go, or Rust. I can go out today and hire someone who understands the inner workings of Python as well as anyone working on the Django team. Anecdotally, as someone who has hired for Elixir roles, this seems difficult to do in Elixir, and I don't know why this is. I have been trying to understand why I have this perception and whether this perception is correct for literally years now, and I haven't been able to figure it out. (Strangely, Erlang on the other hand almost tilts too far in the other direction, with a ton of senior-level people and very few junior or mid-level.)

I could say more but it's probably better that I just leave it at that. I also want to say that I write all this as someone who really loves Elixir but wants to be honest about the issues that I have seen hamper adoption at the companies I've been at.