PlayOnline is a backend environment that supports multiple games, like PSN and Xbox Live are on the modern consoles. It handles the same tasks those platforms do, linking billing to an account, managing a global friend list that lets you see what friends are playing, and a communication option to those friends. Yes, the other 5 applications supported by the platform have shut down, but considering the platform was made for PS2, intended to work with games from Squaresoft, Enix, and Namco, and done before Xbox Live and PSN were a thing, it's pretty impressive. It's also hard to disentangle the functions from it and make the game launchable on its own, though they have shifted most of the account management to the web interface instead of PlayOnline. Given the churn on the development team, such disentablgement isn't going to happen with only a month or so of major development left.