Quoting sareth01, reply 22Multiplayer Sins is the most alive it's been in years, thanks to steam sales.
Many people griped about this game going to Steam, but it's been the best thing that ever happened for the online multiplayer aspect of the game.
That is correct.
Still, offering a version that does not require Steam would have been great.
As MP is handled by ICO, a non Steam version of the game would not have hurt the - very helpful - steam sales.