1. Development of compiler and core libraries strictly BDFL driven (at least used to be)
2. Fixing some important compiler/library bugs takes years
3. No way to host private package repositories
I still use Elm personally, although these are very valid concerns.
4. The language is still unstable. Porting our code to the next release could be a huge task.
5. Elm + JavaScript is generally painful.
6. Few libraries, some of them unmaintained. Combined with the near-impossibility to use JS libraries from Elm, it would increase our work too much.
I would never use such a thing in production.
Getting rid of kernel modules for everything others than core packages in 0.19 made JS <-> Elm interop even more painful and broke some apps. I forked the compiler [1] to support that, although it is not upto date (still stuck at 0.19.0)
That's kind of related to the dictatorial community management. Relatedly, you still can't write a generic sort function.