Those arguments don’t really hold water at all. Games are more than just the sum of their parts. Making all of the pieces work together cohesively is a huge amount of work. Every game is a complex web of features and content. Any given feature is dependent on a bevy of other systems and features and any failures can easily cascade into catastrophe. One of my acquaintances works on the Call of Duty franchise - she told me that they often have difficulty porting features between the single and multiplayer versions of the game due to the way the technology is set up. It can take days of engineering and scripting to bring a feature from DMZ to regular multiplayer or another game mode.
Got a burning question you want answered?