I think SQLAlchemy vs Django ORM was a 2007 blogging topic: https://www.b-list.org/weblog/2007/sep/04/orm-wars/
Now of course it is not Django's responsibility to unite the Python ecosystem in the first place and they can value other factors and arguments as they see fit.
Although this very thread shows that there might have been something to it.
> a sizeable share of the community deems inferior
Well, yeah, SQLAlchemy is standalone, you can use it in a lot more situations than Django's ORM in practice, because you're not tied to using it in a Django site. But that doesn't mean it's "better"