I was thinking about this recently as well and how despite the fact that i'm supposed to be searching for my kidnapped son, I just don't feel the pressure as a real parent might. It also got me thinking about the main story in FO3 and how there's already a story for you when you leave the vault. What if they did something similar to how Half-Life started where for the first 10-20 minutes of that game, there was no story? You were just starting another day at work and going through that normal routine, and THEN something happens to trigger the story. In FO4 there could be the same circumstance where you awake from he cryotubes and manage to escape the vault and then just wander for a bit, before this huge main plot begins to unfold for you.