A lot of the planets around the core worlds are terraformed; insofar as we know, actual earth-like worlds are extremely rare. It makes sense that you'll find more earth-like planets around the core-worlds than not; in addition, you mentioned finding earth-like worlds around the core worlds with a 0 pop well, grats, you found a new planet to colonise.
Point is, the further you get from core-systems and colonised space, the more rare earth-like planets become. You've about 400 billion stars to explore, stop complaining and start exploring; you know, I think your actual complaint is less about the lack of earth-like worlds and more about the fact that you won't be making as much as cash as you'd hoped you would. ;-)