It's popular because OOP is the only thing most people know and understand better than any other paradigm and has been a staple of "reliable software" in big business.
TypeScript supports both FP and OOP styles of programming. And it doesn't add any new OOP features on top of JavaScript.
One might argue that interfaces are an OOP feature that TypeScript adds. That said, you aren't forced to use them.
Interfaces are excellent for defining structures in both FP and OOP paradigms in my opinion. They simply describe the shape of data. This is useful in most situations I can think of at compile time.