Well, there is an easier response:

Every JavaScript developer is already working with TypeScript. So, they do not need to move, they already are there.

Since the inception of Angular 2, TypeScript is designed to be a superset of JavaScript. Or in other words, every JavaScript code is a valid TypeScript code; the only difference is that with TypeScript you can add more fancy stuff. Although that, once it is compiled, all that fancy stuff is stripped out, and returned to JavaScript.

That is something that some people take a little bit to understand. There is no sense of choosing one or the other. It does not matter which you choose, both are the same, with one kind or other kind of comments.