Yeah, duh. The argument is that there is a group of people who wants types and write libraries. Before they used JSDoc, which is effortless to use from JS, as it's just actually vanilla JS. Some of those started using TypeScript now for everything, including libraries. If I want to use those libraries, I need to fork the project and rewrite them to vanilla JS, something that was not needed before. Or find a different library/write it myself.