To sell it 4 times. (Six, if you want extra episodes too). It was trendy then, so they tried to sell everything in parts. All then current platforms (even PS Vita) knew how to download additional content, so they got it as episodic story. It was more difficult with the first part, because it was originally on nintendo 3DS, and there everything is on a cartridge, so even though the story was conventionally divided into episodes, everything was sold at once. If you only have the first episode, Penal Colony, there is a lot to spend your time with, but in sum, of course, the full story is the four main episodes.