[rapsey]

For a technology to become widely used it usually needs one or more of these factors when it is released:

1. A big company that adopted it in a major way or created it (Go, Java, React).

2. A very low barrier to entry (Go, node.js, Python).

3. A major leap in productivity compared to alternatives (Ruby+Rails, Python).

[arrowsmith]

I'd argue that, once you've learned how to use them, Elixir/Phoenix absolutely provide #3

[ativzzz]

And that's the big barrier.

Rails/python are immediately productive and you need minimal knowledge to start reaping benefits.

Of course once you start doing complex things you need to obtain that knowledge but it can be a gradual process

[czbond]

Great breakdown. I hadn't really thought of each of these in this manner

[sergioisidoro]

I would add

4. A critical mass of community packages and open source ecosystem so you don't re-invent the wheel for non core things (eg. Javascript, Python, Rails)

[endisneigh]

Node.js is all of these, which is why it's one of the most popular stacks.

[arccy]

these days you also need a half decent ecosystem around it if you want to get past the early adopter hype peak