My suspicion is that the king is an asshole and made it so only people with the royal pass of entry can enter the ruins.
He probably suspected the MC to get a lesser pass from a merchant or something.
So now every common person who used to enter the ruins are not allowed.
That or this particular ruin has had something inside of it make it a higher security clearance...
But that's not as funny.
@xyzzy idk if I read it wrong, but the way I see it is that the book has info on everyone, but only actively tracks where important people are and what they're doing.