Earlier quoted context omitted.
Last time I tried ty and pyre they weren't particularly great with a Django codebase, I'm sure ty will get there at some point, but if this handles django-stubs without any extra faffing, that's one potential selling point. I did have the same thought as you at first though, and only carried on reading when I spotted that it was from the author of Jedi.
Both ty and Pyre are in development, so maybe the answer is just "this works and they don't". But they do promise to work eventually, like end of year if I recall correctly. I don't know what makes Django special in this regard though - is it the ORM models that don't work well with the typing spec or..?
The ORM models do not work with typing at all, you basically have to make a lot of magic work if you want to support it in a type checker (especially if you want to work with reverse foreign keys). Generally type checkers do not just support the Django ORM. For Mypy there's a plugin that works pretty well, but uses runtime information, which further slows down Mypy.