Budget
I would wonder how that trace overlays with the show budget over the years (in normalised terms of course)? Presumably the Earthbound episodes would be a bit cheaper to produce (with set re-use or just location work) compared with specific sets and costuming for more alien stuff.
And with all these swings to the left and jumps to the right, are you sure we're not just doing the Time Warp (again)? ;)