So I've been getting these quite often when choosing familiar-type glyptic on Herculean gear.
Even if we ignore the fact that Charm is useless now days for a number of reasons (does not scale with item level, prevents trust summoning, and all relevant content takes place in a battlefield or confrontation which prevents interacting with charmable monsters)...
BST IS NOT ON THIS SET! So why does this exist? This is the only instance I know of where you can get a trait that's completely unrelated to every job on the set (not counting dark matter). All it does is further lower the chance of getting a decent augment in that slot.