I don't understand the inconvenience. Isn't it just adding `attrs` to requirements.txt once for the whole project, and then you get more features ever after?

Simple != easy. It is easy to add another dependency, but you've just added another piece to the puzzle that needs to be maintained.

That assumes you have a project. Some people write scripts in Python to use in the shell.

venvs work fine in the shell. See pipsi for automatic creation/management of the necessary venvs.

Some people write simple programs which they then (say) email to others, or put on a blog post, or on a gist, or a SO answer.

If the simple program depends only on core Python, then they don't also have to say "oh, and also install ...".

It's one more thing that can break in production.