The reason is online multiplayer. It was originally introduced as a way to add replay value,butit became a main selling point. This shifted focus away from single player and shifted it towards the very competitive multiplayer. The competition of online multiplayer made things frustrating and not fun. Devs need to give singleplayer more focus if they wish to keep games fun. Hopefully,games like Infamous 2 and Medal of Honor will shift the focus back to where it belongs,and defeat the frustration of forced multiplayer.