My theory is that it’s one of the core parts of the night elves the lore team haven’t revealed in detail.
The night elves are very thin in detail. We know hardly anything of the Moon Goddess except a lot is done in her name and the priests follow her.
The star stuff is shown in game a lot, in the magic of the priests, druids and mages offensive stuff, in the greeting and motiffs… it hints to a large aspect they just haven’t fleshed out.
The astrology towers of the night elf civilisation we see speak of them, and we have as much Star symbology as moon just not much depth shown.
My suspicion is the major part of this identity is part of Night elf civilisation which has been on a 19k year pause due to the long vigil, and when we get a proper night elf story after BFA that will show proper night elf civilisation returning. We will see much more of this.
There is a reason Night elves are still purple skinned and silver eyed and stilll called Kaldorei rather than children of the forest like sons and daughters of Cenarius. And why they aren’t green skinned, eyed and only 1/3 of the hair colour themes match the forest colour, the rest reflect the arcane, the night and the stars/moon.
I suspect we have seen the detail on the Druidic nature life, but not the moon priest related life nor the core Star civilisation. Suramar is our only glimpse of that and it hasn’t given much detail.
But even then. The culture that stagnated is the Kaldorei invasion pre sundering culture. They just stuck in that phase. When you really think about it, the pre sundering culture had many phases. The phase around the time of the invasion is very different from the one when the cities were at their height and addiction hadn’t set it, which would have been different from the time when they were being built and the Kaldorei were expanding defeating their enemies with the Arcane well power and the night warrior ritual.
Also different from the phase they started really getting a handle on the arcane.
This is why although it is all Kaldorei culture. The nightborne would be different from the Farondis culture and likely different from the shen’dralar culture and all of these were significantly different from the high elves and totally different from the Druidic and priest long vigil dominated.
Bear in mind the priest and Druid culture were also different cultures