The armor that has dropped during the recent events and the protection armor that drops off the chest makes it have the rarity it still contains up until now. If protection would be a more common thing, it would throw away the rarity. Eventually, the armor would break or be disenchanted and as such, become more rare over time. By using these events the Staff can ´refresh´ the armor and return it to a acceptable rate of rarity. As such, it would not be wise to have enchanters be granted the skill to do so as your suggestion applies. Instead, it would be more game-breaking then you'd think. It would, also, mess up the economics of the protection armor, leaving people with less money, which could leave the less satisfied. To put it all simply, if you make protection armor common, it would affect a variety of game expierences such as events and chest hunting.