It's not so strange.

Pre-LLM: Nix is "high effort, moderate reward". The cost is: you have to learn a tool which does things apparently completely different to how other tools do things.. you have to put up with a lot of friction, pay all the pain upfront, and the benefit is that may be later it's easier to get the package again.

It's just not a practical trade-off for most developers.

With LLMs, the cost-benefit trade-off changes.

You can use this cloud provider's LLM to get you a good result. You get the benefits, and the cost is 'just' "ask the LLM to do it".

Similarly: it's easier to assess whether produced code does the right thing, than to come up with that code from scratch.

Without LLMs? The inaccessibility also comes from being a niche tool. Not many use it, so not many software projects accommodate it or consider it, and you might have to come up with workarounds yourself.