There is of course no hard reason for not using the global scope. I just often have enums (or other types) that are very closely linked to one class. And it makes sense to me then to have a TypeAlias in that class so that I don't have to import the enum separately.

For normal classes, the nested TypeAlias works completely fine in the type checkers I tested (pyright and mypy). It's just dataclasses that are the problem.

But I see now that there is a general wish to keep the implementation of dataclass simple, which I can understand.