I think their logic is "We want to give Dragoon better innate defenses because it sacrifices some amount of offense for some amount of utility (the amount varying by support job). Defensive abilities are also a form of utility, so we're enhancing those to go along with this theme."

Which makes sense but moves Dragoon more towards Dancer and Blue Mage territory. I think most Dragoon players would prefer MOAR! POWAH! instead.