Actually, I mentioned long ago in one of the books that the box only works once. Use it a second time and you get hives. Or possibly dandruff. People in this culture of psycho-babble and Disney happy endings sometimes forget that it's the persistent conflicts that make characters interesting. People are as interesting as their limitations.
People are complicated and messed up.
And that's mostly a good thing. At least he's not dull. I would really like to see Tobias discover his mother. It seems like that. But if they did leave America to protect the other continents the Yeerks could quickly take control over it.