Because at the end of the day TypeScript is still Javascript and it's still bad. Just has some verbose formats to try and make weakly typed language (javascript) appear to be strongly typed. It adds more build steps to what shouldn't be there; build steps make sense for apps, they make much less sense for libraries.

https://dev.to/bettercodingacademy/typescript-is-a-waste-of-time-change-my-mind-pi8
https://medium.com/@tsecretdeveloper/typescript-is-wrong-for-you-875a09e10176

We use TypeScript for our node.js backends.

We had two that started out vanilla, but it became too painful to maintain.

It was used pretty frequently for back end APIs too

I wrote some TypeScript modules to process a bunch of documentation in markdown to a ton of output formats via pandoc + latex.

No real reason for it, except that I was able to start with the export module of a node-based thing written in JavaScript and iterate from there until I had a working system in CI/CD.

It can with some glue code that you better be writing in TypeScript if you care about code quality.

(As far as I know, it can't manipulate the DOM directly. Maybe things changed in the past couple months since I checked, but I doubt it.)

WASM allows arbitrary code execution in an environment that doesn't include the DOM... however it can communicate with the page where the DOM is available, and it's trivial to setup an abstraction layer that gives you the full suite of DOM manipulation tools in your WASM space. Libraries for WASM development generally provide that for you.

For example here's SwiftWASM:

let document = JSObject.global.document

var divElement = document.createElement("div")
divElement.innerText = "Hello, world"
_ = document.body.appendChild(divElement)

It's pretty much exactly the same as JavaScript, except you nee to use JSObject to access the document class (Swift can do globals, but they are generally avoided) and swift also presents a compiler warning if you execute a function (like appendChild) without doing anything with the result. Assigning it to a dummy "underscore" variable is the operator in Swift to tell the compiler you don't want the output.