Ah, I hadn't noticed that, since the toon I checked with has the faction... so the faction requirements weren't visible.
So it ties back into 'only crafters can buy it'... so it's not something crafters can commision for non-crafters. Also, since it takes adventure currency, it's not like 'pure crafters' can turn their crafting tokens into plat by making the runes and selling them to adventurers.