Not seeing a "why" here, though. If you like TS, go use TS, but if you want type checking then JSDoc does that job rather well and forces you to treat documentation as a first class citizen, too. With the obvious bonus of not needing to be compiled: the code you wrote is the code that runs, while having all the features in place to perform type checking. It just goes about it in a different way.

The goal is type safe code, and there are multiple paths that get you to that goal. Pretending that TS is the only, golden path and everyone else is hopelessly wrong -requiring hyperbole to mock even- suggests having lost sight of the actual goal itself.