C'mon guys, we all know that the real enjoyment derived from this series will be from the rage-filled commenters below the video. Remember the spitfire under two games that a lot of people hadn't played?
Imagine what the comment section will look like when so many people have spent dedicated hours in this thing. Glorious.
If they created and implemented multiplayer it probably would have been a $60 game, and it probably would have been very poorly received because of it. They have most likely profited more from taking the road that they did.