At first, I was thinking Town Hall was retiring for a few reasons already stated: price point made it the slow seller of the group, too much shelf space, etc. Then I started to think about production costs, part number reduction, etc: according to Brickset, Town hall has several "rare" bricks... part numbers used only in Town Hall, or used in only a few other sets (many of which are already retired, or who's days are numbered). If they dropped the Town Hall, they could drop quite a few part numbers. Looking at part numbers shared with less than 3 other sets, I found:
6000644 shared only with Arkham Asylum
6022319 shared only with Santa