It is a mistake. The only other economical truck out there is the Tacoma with the 4cyl engine. And for some reason nearly every Tacoma I ever see on the road or on the lot is a V6.
I've read one reason stated is that the world Ranger is too close to the size of the F-150 to really carve its own market. That I might agree with a bit. I also read that I think it was 90% of all truck sales in the U.S. are full size models, making it unprofitable to sell that ranger here. Maybe if there was more choices in small trucks and models that truly got good fuel they could sell more in that class.