Developer happiness includes all facets of development IMO. The language, 3rd party packages, the overall ecosystem, the community, etc..

Elixir isn't really in the same ballpark as Python and Ruby for package support. Lots of 3rd party vendors don't have official SDKs for Elixir and having to recreate certain components of those SDKs manually can be very tricky. This is especially true for payment gateways like Stripe, Payal, Paddle and others since there's gory details about certain things aren't as easy as making an HTTP call with a token. So you end up having to recreate these things from scratch because most community versions are abandoned due to them being maintained by 1 or 2 people who stopped using it.

Also, LiveView's APIs keep changing. The amount of churn was out of control for a few years where it felt like every few months you had to make drastic rewrites to keep up with it all. At the same time the docs are very minimal and community support through blog posts weren't there in the same way they are for Rails and Flask. It felt like you were on your own to solve everything in a fast moving world with an ever growing API.

Then for the language, Elixir didn't click for me, even after writing 10k lines of code. I felt like I could get pretty far and understood enough to get most things done but I felt like I was getting stonewall'd quite frequently and couldn't solve certain basic problems after exhausting all pre-existing resources (my brain, docs, blog posts, open source projects, etc.). I don't feel I have this same issue in Python or Ruby. There's such a big community that nearly everything can be found, or at least get you to the point where you can apply something to your domain without asking in chat for help.

A good example is https://github.com/josevalim/nested-map-reduce-traversal which is something Jose and I worked on a few years ago. If he didn't step in and provide an example on how to do what's essentially a nested loop while modifying a counter in Elixir I would have had to stop developing my project. I still have to step back and spend a full 5 minutes trying to mentally parse his solution where as the Python and Ruby solutions are immediate with no effort.

When trying to build a pretty big project, these routine blockers or having to spend 3 hours (or 3 days) down a rabbit hole vs just doing it in a few minutes make a big difference -- this is also after spending months learning the language and ecosystem already. You end up getting fatigued from having to build so many libraries to get to the point where you can work on your main's app goal and it's demoralizing getting hard blocked. There's also this pit in your stomach that's concerned at how quickly you can get stuck in a way that you can't self-resolve. When trying to build a business, these are all very dangerous things.

You put all of that together and my happiness level for Elixir was kind of low.

It's nothing personal, just my opinion. I think it has good ideas and concepts in places but it didn't feel like the juice was worth the squeeze for someone like me who didn't already have many years of functional programming experience beforehand. Flask and Rails are both fast enough where you can build a million dollar a year business on a single $40 / month server with tens of thousands of customers. You can still get p95+ <= 100ms response times from your back-end in this scenario and both tech stacks have a good story for using websockets nowadays. Thankfully Hotwire Turbo is back-end agnostic which means you can build really nice feeling front-ends with any tech stack with minimal JS. I'm really happy DHH pioneered this pattern with Turbolinks which evolved into something wonderful.