Elm is still way too immature. You either end up rewriting a lot of code that might otherwise already exist as a library or you simply cannot use features because they don't exist. If you hang out on the slack channel you'll get an idea of what the language can and cannot do right now. It's also worth remembering that it's a technology that doesn't have the weight of a big company behind it so pace of progress is relatively slow.

I would probably agree with your first 2 hypotheses. However I don't really see any momentum against Elm. Just the opposite in fact. There are other projects that have the same kind of goals such as Purescript or GHCJS but Elm is the one with the momentum.