Is there a reason those features weren't added to data classes?
I don't know much about attrs, only professionally coming to python since 3.7, but I'm not going to bring it in if there's something sufficient in the language
Not really, other than they decided to keep data classes very minimal, as standard library comes with maintenance costs (you can't get rid of a feature once you add it), so they kept the strict features, since everyone uses those, and not the complex validation features.
