Errrrr...this is a new one, as this is not a reprint, which you have implied. There are two reasons as to why they used Jace for this. The first is that Jace is a recurring character in the magic storyline. He's actually in Zendikar doing stuff, so having him as another card obviously makes sense. The second is that the rules dictate that you can only have 1 kind of Jace on the battlefield at a time. It's kind of dumb to have that rule when you don't make the same planeswalker at least a couple of times to make the dilemma to choose to actually be there.
So far of the planeswalkers that have arrived since its original print 2 years ago, only 3 planeswalkers have gotten a second card. At present, this block has had 2 reintroduced planeswalkers and 2 new ones.