I'm sure you know more about this than me, but EF works fine with SQLite for a project I work on. There are limitations, but I think there's a difference between the idea of EF deliberately not implementing some features for SQLite and SQLite itself not having support for some EF features (which is the reality I'm familiar with).
SQL Server is the flagship database project on the Microsoft side and that team surely has some imperative to facilitate the EF vision. It simply must be less of a priority for the PostgreSQL and SQLite maintainers to do so. Is that really a valid dig on the .net ecosystem, though?
Incidentally, I'm seriously considering dropping EF. The ability to apply migrations is nice. I find the means of authoring them to be arcane and capricious. Not having to write every simple query is nice, but it gets really hard to do complex or high performance stuff. After a decade of using this thing, I find myself fighting the Entity tracker more and more and now I'm seriously questioning if it's really all worth it.