It uses a huge amount of what I’m terming “getattr bullshit”: many/most fields of ORM objects are only determined at runtime (they’re technically determinABLE at
early runtime during Django initialization, but in practice are often not actually visible via reflection until they are first used due to lazy caching).
What fields are present and what types they have is extremely non uniform: it depends heavily on ORM objects’ internal configuration and the way a given model class relates to other models, including circular dependencies.
(And when I say “fields” here, I’m not only referring to data fields; even simple models include many, many computed method-like fields, complex lazily-evaluatable and parametrizable query objects, fields whose types and behavior change temporally or in response to far-distant settings, and more).
Some of this complexity is inherent to what ORMs are as a class of tool—many ORMs in all sorts of languages provide developer affordances in the form of highly dynamic, metaprogramming-based DSL-ish APIs—but Django really leans in to that pattern more than most.
Add to that a very strong community tendency to lazily (as in diligence, not caching) subclass ORM objects in ways that shadow computed fields—and often sloppily override the logic used to compute what fields are available and how they act—and you have a very thorny problem space for type checkers.
I also want to emphasize that this isn’t some rare Django power-user functionality that is seldom used, nor is it considered deprecated or questionable—these computed fields are the core API of the Django ORM, so not only are they a moving target that changes with Django (and Django extension module) releases, but they’re also such a common kind of code that even minor errors in attempts to type-check them will be extremely visible and frustrating to a wide range of users.
None of that should be taken as an indictment of the Django ORM’s design (for the most part I find it quite good, and most of my major issues with it have little to do with type checking). Just trying to answer the question as directly as possible.