The problem with an unsound type system like TypeScript's is that once a value of an unexpected type has snuck through a soundness hole, it can end up anywhere in the program, even in code that seems fully safe.

(Also, it means that you don't get any performance benefit from static typing your program.)

But they decrease productivity. And I seriously think many teams don’t track the time sunk for fixing bugs / defects properly and they overestimate their productivity, especially the initial productivity boost from not having to think about types.