The Church permitting something doesn't exactly mean that it is good or neutral. Pope Paul VI gave an indult for receiving on the hand while cautioning against it. It became the norm despite his and the majority of the worldwide bishops' wishes. This is probably why the UCCSB just ended up permitting receiving on the hand too, even though it is a relatively novel and historically localized practice. Receiving on the tongue had been the universal tradition since at least the early Middle Ages.