I can get where you're coming from, and it's fair comment. Personally I don't believe that they're creating things then purposefully putting it to the side to release later. It seems that the development process often goes wrong somewhere, there are numerous assets that don't fit with the new story so need to be dropped. I'm fine with them not being discarded and instead being brought back later, further developed or altered then fitted into an update/DLC/expansion etc... It'll save the time needed to create something entirely new when something suitable was already there. In turn that should release some development time for other work.