C++ was originally a layer on top of C. The first C++ compiler, "cfront" was actually a transpiler to C.
There is nothing preventing TypeScript from becoming "native" in a similar way.
If you are going to mention enum and namespaces, the team considers them a design error, and only keeps them around due to backwards compatibility.
I never thought of Typescript (TS) that way. I believe TS is a language addition that enabled smarter JavaScript linters; TS is not a linter program per se.
However, TS is more than that now. The extra annotations enable optimizing transpilers and even compilers (to WASM, for instance). This makes TS much more than just a better linter; I think of TS as a better language.
Java IDEs were taking advantage of them for web development workflows, before VSCode came to be.
Also VSCode main architect is one of the Eclipse original architects.
Theres no reason to ship TS to an end user browser.
As things are now, developers write code in TypeScript, then debug and update code in Javascript. It might not be much of a reason, but a single language throughout is surely easier on developers and maintainers.