Because they aren't still selling 2013 Rangers. To North America it is an all new design.
I agree, it's not impressive just like the Colorado and Canyon are less than impressive too me. But much like GM, Ford see's a potential to make sales in the market, so they took it. Sales in the mid size truck market dropped when GM, Ford and Chrysler got out of it. Then GM came back with the new Colorado/Canyon, and saw sales. So Ford scrabbled and brought the Ranger back and Chrysler(now Fiat) finally brought the Gladiator. Give it 10 years and they'll pull back out of the now flooded market again. The same is coming for the over flooded CUV market.
The surge in CUV's show that manufacturers haven't learned anything, they continue to flood markets with the same things instead of diversifying.