For prestige brands, Why social media doesn’t work?

So, it is official, that social media is of little use for the prestige brands to attract new customers – as evidenced in the recent L2 report after studying nearly 250 prestige brands, saying that less than 0.01% of new customers have been acquired via Twitter, and no more than 0.25% via Facebook.
Yet it did not tell WHY, and whether there could be a way to turn this around.
In China, on the predominant social media – Sina Weibo – the hybrid of Twitter and Facebook, the situation is not much different – although there is lack of L2-like research results, as the long term observer of …