So if you start paying the Andean villagers a lot of money for vicuna wool, all their neighbors will start raising vicunas, because who doesn't want to get rich raising sheep in the mountains? Then the market would be flooded and nobody would pay top dollar for not-so-exclusive vicuna anymore (the villagers probably know all this, but don't have access to direct-to-consumer marketing for more competitive pricing - get them a Starlink Terminal and ah, err, Tiktok account?
Fashion is a funny business, more about social science than economics. Incidentally wool demand might be rising due to microplastic concerns over synthetic fleece clothing.
Vicuñas are dromedaries, they're not closely related to sheep. You can't just raise them. They're the wild animal that was domesticated into the alpaca. They're not a domesticated animal, they are a wild animal with very poor temperament and locals do not keep them, they capture wild vicuñas to shear. There's no realistic way to flood the market, the supply is limited by nature.