Part of the reason countries just keep making weapons beyond what they need is in order to maintain their manufacturing base. It takes a lot of special tooling,

Part of the reason countries just keep making weapons beyond what they need is in order to maintain their manufacturing base. It takes a lot of special tooling, materials, and training to make a particular weapon. If you let it lapse, getting it started back up might be less worth it than just designing a new one. Just adding an additional product when it looks to be more profitable might mean having to buy more land, building a new building, starting with all new workers, etc. Unless the previous product is really profitable and stable, it's likely they'll just retool and retrain for the new product.