I think they do that so that you can use an inside the box frame feeder and only need to pull one frame for it to fit in. I don't like it myself, as I don't use inner frame feeders, and it causes the bees to draw the wax out further on the 2 outer frames (I push all frames in to the center, so equal space on the two outsides). With the 2 outside frames over drawn on one side, I find it difficult to be able to move them to any other position in the hive that is not an outside frame position. i'd much rather have the boxes all with proper bee space. My only easy fix that I can come up with is to make follower boards to slip in to take up the space, but that adds weight and besides, I'm just to lazy to do the extra work.