I have used elm for a smallish (10 people or so?) team writing software for revenue, and regretted it. that was 4-5 years ago. my reasons had a lot to do with the community around elm, which other comments allude to. This group had different concerns to mine:

  The thing that ultimately tipped the balance in React’s favour for us was that we acquired another company whose entire codebase was written in React, and whose team knew nothing about Elm. Overnight, we went from a company that was writing about equal amounts of Elm and React (and which might well have decided to double down on Elm) to one that was writing about 75% React.
  
  By that time, TypeScript had grown to be capable enough (and developer-friendly enough) to balance much of what sold us on Elm originally: a usable type system, good-enough error messages, etc. React had baked in some more useful state management primitives that roughly matched Elm’s “batteries included” state management.

if you like the ideas in elm but don't want to commit to it I'd encourage you to check out elm-ts (https://gcanti.github.io/elm-ts/). It has a little bit more boilerplate than elm (I find elm to be quite verbose already!) but a better experience for individuals and teams overall, I would say. It's a good example of how "TypeScript had grown to be capable enough (and developer-friendly enough) to balance much of what sold us on Elm originally: a usable type system.."