This question has been discussed in the comments before, but has never been the subject of its own post. The two direction rotation is an occasional source of frustration for many people who would like more flexibility in designing their town, so this is a question that often comes up.

There’s no real answer to it, except to say that that’s the way the game was designed. You can see it not just in the building rotation, but in the angle of the town on your screen. And all the building image files in the game only show two rotations for each of the buildings or decorations.

The 2-D approach is actually part of the charm of the game and very much in the spirit of how the show is drawn. To change it part way through the game would require some major re-design work and substantial rewriting of the code. Perhaps at some point in the not-so-near future, there’ll be a re-launch of the game in an interactive holographic 3-D version somewhere early in the next decade! But until then a 2-D 2-rotation New Springfield is what EA and the game will continue to give us.