So, yeah, you can't make your friends create characters who care. I think that's probably okay, I think you can play the game anyway. Your job is to create the world, make it interesting and unstable, and then play to see what happens -- not to threaten the PCs or hit them where they care or anything like that.
Maybe what happens is, the PCs don't get involved with anything much, they sit around and hunker down, and they rebuff any NPCs who come near. Okay! You're playing to see what happens, and this is what's happening. I don't think you have any duties beyond that. It won't be fun for long, but that's not your responsibility. "Hey, so, if you aren't going to do anything, this is all it is. Want to step up, or should we call it a game?"
That's my take. If they don't want to play the game, you can't make them.
If they do want to play the game, but they want to play dangerous loners, that's cool, that's their call. Remember to make PC-NPC-PC triangles with named, human NPCs, and the rest too. Then whatever happens, you've done your job.
-Vincent