I understand the appeal of this game, reading instructions from a manual at someone while they try to defuse a bomb, but i already know that convincing my friends to stare at a pdf while one of us plays a game wouldn't engage them enough. If players could join the defuser in the room and scream instructions from within the game then at least everyone is in a video game together, i guess you could figure it out in a + teamspeak + adobe reader + steam broadcast situation but other players arn't supposed to see the bomb right?
If a party could play in an online room the person defusing could rotate simply instead of taking it in turns with loading up the game or loading up the pdf... it would also mean each player has to own the game which would be positive for sales i'd have thought.

There's obviously reasons why it wasn't done, it's just my group of friends has a ton of fun with co-op games that do support online.