You don't have to use them, docker has flags to disable things like network isolation. If you want to go deeper systemd-nspawn doesn't isolate anything (network, pid, user, filesystem, etc.). And if you are some anti-systemd zealot the plain old chroot command does what you want too (and has done so for decades).

Except none of those solutions are package managers, are they? The thing that's nice about nix is that you can just specify which packages you want by name, and easily get them in your path.

My thoughts exactly. Container-based development environments has a Cygwin-like clunkiness to it. But even clunkier because of the default lack of access to the host system, and the additional burden of having to manage multiple containers.

Just to be clear, Cygwin is a great project. But it's not something I'd actively choose over a native Linux system if I had the choice of operating systems.