As soon as a viable alternative pops up for nix which has all the advantages of current incarnations - of which 'open' and 'free' are but two of the more important ones - they'll take over the world. Until such a time we'll keep on using our nix-hammers just like carpenters have been using their hammers (nowadays often driven by electricity or air) because they work well enough for the intended purpose, the occasional blue thumb notwithstanding.

The thing is, we didn't move on.

We hacked most of the advantages of anything newer back into them, in a haphazard way, and kept them because as a sibling pointed out, nowadays they are open. And openness is a very important feature. (It's just not why they were adopted, people cared so little about openness that Unix was born open and mostly closed up later.)