The price of buying a new (or used) box vs. the price of "Bricklink"ing the parts is usually pretty much in favor of the former, which makes sense since the latter involves more S&H fees.
In additions, new moulds or new colors for existing moulds come up all the time (yet new moulds are all designed in the same system, so that they increase the versatility of Lego rather than Playmobil-izing them). Therefore, advanced fans who design their own creations and buy bricks in bulk do get lots of new Lego boxes. For example the VW Beetle model, besides being really cool in itself, had a lot of azure bricks, including many shapes that had never been realised in that color. Likewise for some Architecture boxes.
 "New bricks are too specialized" is the Lego version of "HN is turning into Reddit"