That's because (a) these are not historically type-inferred languages–runtime typechecking doesn't count as type inference–and (b) the gradual typechecking approaches like Mypy and TypeScript often have a lot of type inference issues which force people to try to overcome them with manual annotations.
In languages with even reasonably good type inference you'll find that the idiom is not to annotate types at the very least inside function bodies. And in OCaml, which has principality of type inference i.e. the types it infers cannot be overridden and corrected by manual annotation, the idiom is to not annotate implementation files at all.
In languages with even reasonably good type inference you'll find that the idiom is not to annotate types at the very least inside function bodies. And in OCaml, which has principality of type inference i.e. the types it infers cannot be overridden and corrected by manual annotation, the idiom is to not annotate implementation files at all.