Both, learning curve was difficult and is impossible to get resources with good/real Elm experience. Also, you end up with a huge Main file in enterprise apps.
Elm use a different paradigm (Functional Programming) and if you are not aware or have experience with it, it will take long time to understand it. The company later moved to React/TS due the issues mentioned above.
Elm is a small and easy language. Certainly much smaller and easier to learn than JavaScript. You should go through the Elm tutorial. It shouldn’t take you long.