In the past, when Sam was alone, there was stll someone out there he could turn to. Even in the cage, when Lucifer would punish him through isolation, Sam knew he'd be back eventually.

Now, everyone is gone. Sam's got to find Dean and Cas. He's got to stop Sucracorp from exxterminating whole swaths of humans. He's got to find a way to actually kill a Leviathan, let alone all the ones out there. He's got to rescue Kevin and defeat Crowley and find out why he wanted the prophet.

There's so many things that have to be done *right now* and no one but an apocalypse -starting, alleged-serial killing, former-demon-blood drinking, almost human to do it.

It's kind of a downer.