Maybe because, according to our records, this plant is a propagation from a collection of E.H. Wilson. We have it by way of the Arnold Arboretum, which makes sense. We're all a bit wary of barberries in general; they seem to present chemical (and physical?) properties that make them unpalatable to deer and so, are invading natural areas replacing the native vegetation eaten by overpopulations of deer. Haven't seen seedlings of this plant but who maybe different soil, a differnt moisture regimen, a slight shift of temperature and it could begin to spread. So we watch.
Actually, this particular plant is in an awkward location. It's too close to the path and probably too large to transplant with a certainty of success. Amanda has stuck a handful of cuttings and eventually, after we've established a replacement or two, we'll remove it.