Curious to know more, do you think can make a long-form of "why" and a detailed experience? If you have some time, would be massive to compare it with what's the same experience today
The biggest differences between Elm and ReScript/ReasonML as language features are bindings, JSX and purity. Bindings in Elm are cumbersome and limited (on purpose) while in ReScript/ReasonML are easy, more feature complete and a little more fragile. JSX is exactly as React, while Elm doesn't have it; some people prefer it, some people don't. I love it.
Purity in general terms makes Elm more strict while ReasonML/ReScript allow impurity when needed, still most APIs enforce functional style, immutability and proper data structures.
Regarding community, there's drama everywhere not sure If I can do a good job here. Maybe community size Elm is much bigger than others, but they need to reinvent most of tooling that is done in JS and ReScript/Reason takes advantage.
I encourage to not rely on anyones opinion about what's better, because you listed 5 languages with opposite directions.
Try it out yourself and decide based on users/team needs. Cheers.