A big problem is that elm has questionable stability as a project. It's mainly one person, and not a lot of mainstream usage. The biggest projects mentioning elm are ones related to the main programmer.

Typescript on the other hand has had massive growth and has been adopted by a large amount of libraries. Now, web ts/js libraries usually suck but it still speaks to the overall health of the language in a community. Even then, typescript still only has a very small percentage of usage.

Elm is basically a rounding error on some of the surveys I've seen.

Long term support, tooling, etc are often much more important for languages past a threshold. Typescript as a language may not be super exciting. Typescript as a technology is wonderful.