I've been somewhat surprised that CUE bills itself as "tooling friendly" and doesn't yet have a language server- the number one bit of tooling most devs use for a particular language.
Tooling friendly can mean different things to different people. Similarly, different groups of people have different priorities.
It has always been clear that LSP was high priority, but we have many other high priority work that also needs to be done. Most of the work that we do is driven by feedback and demand from the community.
Additionally, we want to do the LSP right instead of quickly hacking something together. That requires more work than one might think.
While CUE has not reached 1.0 yet, people definitely use CUE in production and we work hard not to break any of their code. I can assure you LSP is missing simply because we had other things to tackle first and not because the language is unstable in a colloquial sense.
I'm assuming it's becaus CUE is still unstable?
Anyway, if others are interested in CUE's LSP work, I think https://github.com/cue-lang/cue/issues/142 is the issue to subscribe to