Probably because most people would not pick the 4-cyl for a 1mpg improvement, so it has to have something else going for it.
If I were to get a 5th gen, I'd pick the Limited because of the FT 4WD system and the creature features, but I hate the cheezy Cadillac Escalade bling that it has. The SR5 and TE looks much better, but I don't like the PT 4WD system on those. I guess Toyota's back to the roots design doesn't make on trim particular standout over the next as the "better" choice for me. BTW, I hate it when they do that. I prefer they build a top of a line model with everything the lower trims have but the kitchen sink.