I see this question pop up quite frequently in lots of different arenas - folks are curious as to what happened to Elm. As a former community member of Elm, I thought I'd act as a historian here and provide a write up covering the big pieces I see. Everything in this post is public already, I'm just putting it together in one place - and will not touch on anything personal to anyone involved. The interesting parts are not about personal matters - but about the natural to and fro of a niche technology.
A niche language has to embrace interop and leverage the broader ecosystem to be viable in my opinion. It’s just too much of a lift for a small community to build everything from scratch ground up. Elm tried to be a completely separate ecosystem that eschews Js stack and actively puts barriers for using it.