What does HackerNews think of kaffy?
Powerfully simple admin package for phoenix applications
Super-simple to set up and it's been perfectly adequate for my app's needs so far.
To answer OP's original question: Django Admin isn't a killer feature because the same kind of thing is available for most other Django-like frameworks, with the only difference being that it's usually a third party library rather than something built into the framework itself.
Just curious, did you try Torch or Kaffy?
https://github.com/mojotech/torch https://github.com/aesmail/kaffy
For the ORM and auto-generated DB migrations, I actually prefer the Phoenix way. Ecto makes it much harder to trigger N+1 queries than the Django ORM, and in practice I find the explicit migrations make people actually think about what they're doing and what to index, so the schema is cleaner. But I could see why someone would prefer the Django way, and I'd be curious to see the same kind of system in Elixir.