Here’s what I’m going to say to you:
The Nelves don’t have a form of central government.
The Nelves aren’t a centralized people.
There were never any strictly understood ‘borders’ that the Nelves held largely because of this.
The Nelves have always been largely associated as ‘living alongside nature’ which often conjures ideas of foragers or wandering peoples.
Not to say that there aren’t Nelf settlements or villages, there clearly are. But their agrarian settlements don’t appear to be the norm.
There’s simply areas they live in predominantly, and places they don’t live in predominantly.
The Nelves do not constitute the same kind of ‘civilization’ that the Roman Empire did, they’re two completely different kinds of people.
You could compare the Highborne civilization with the Romans, but no, there is no ‘central government’ of the Night Elves.
Not to say there aren’t spiritual/religious leaders, or venerated elders and so on… but there is no central power which holds sway over all Night Elfdom in the same way that the Romans had a central government.
The Romans, as with most empires were largely agrarian which created an association of land-ownership and power based upon that ownership. Land, as a stationary concept doesn’t move, and therefore a conglomeration of land ownership has a ‘center’, and borders can be drawn from that land ownership.
Nelves, are never really depicted as agrarian, nor are any of the irl people that their culture takes inspirations from largely agrarian. There is no ‘land ownership’ in the same way that we see among the Romans (as an example). There can be a concept of ‘territory’, but it wouldn’t be based off of land ownership surrounding a central ‘capital’.
In the same way, this can be applied to Tauren as well.
Thunderbluff doesn’t constitute a singular central governing ‘power’, but rather a large meeting place of sacred importance to the people. In a similar way to how the World Trees are presented to the Nelves.