NixOS is unique because it uses the only potent package manager (if we don't count that one reimplementation of Nix). Calling the others "package managers" becomes mostly a courtesy when NixOS enters the picture.
lalala with FS-level snapshots + flatpak + distrobox + a kitchen sink
The same reason why webapps are a bad idea. We've built monstrous browser engines to do fancy stuff to pages in a bonkers language in a sandbox, and the resulting abomination is neither pages nor apps. And now we're like: we have so much expertise in shuffling page parts around to look like they're apps, let's build "real" apps out of them. It's like rejecting headphones and towing a car with broken windows around with you just in case you'll wanna listen to music: it technically works, but makes negative sense.
I can tell that this is written by a girl. Not because pink, not because cake, but because the dang sexist clothing industry has somehow turned even "pockets computers" into a male privilege.
You cah also tow a Tesla with a couple of horses