The thinking has always been to make threads and topics simpler to find, and grouped according to their topic. And because the General Movie Poster Board was becoming a catch-all for every topic, whether it had to do with actual posters or not, there were times when multiple threads on the same subject were created because members didnt know, or didnt want to have to sift and search thru 39+ pages of material there, in order to possibly find something.
Let alone that certain threads have gotten buried and forgotten about, as T said. A few more sub-category boards should make it easier. One click and topics about posters from other countries are all together, same with the board dealing with buying selling, sniping. Or poster sizes. Those common threads are now all in better suited boards.
The moving of threads and topics wasn't (and isn't being) done to make things more complex, dilute the forum, or on some random whim, but to make looking, searching and posting a little more concise, rather than members having to meander thru a General section that was fast becoming the "melting pot" home to every topic under the sun.