This is unreasonably dismissive: the `pip` authors care immensely about maintaining a Python package installer that successfully installs billions of distributions across disparate OSes and architectures each day. Adopting deduplication techniques that only work on some platforms, some of the time means a more complicated codebase and harder-to-reproduce user-surfaced bugs.
It can be worth it, but it's not a matter of "care": it's a matter of bandwidth and relative priorities.
"Having other priorities" uses different words to say exactly the same thing. I'm guessing you did not look at pnpm. It works on all major operating systems; deduplication works everywhere too, which shows that it can be solved if needed. As far as I know, it has been developed by one guy in Ukraine.
Are there package name and version disclosure considerations when sharing packages between envs with hardlinks and does that matter for this application?
It can be worth it, but it's not a matter of "care": it's a matter of bandwidth and relative priorities.