Because if one person is allowed to affect the setting in a permanent way, everyone has to be allowed to do so. Not everyone has something so harmless as a simple fire in some nameless inn; some people have wanted to pretty much raze the town, or large parts of it. As a result, I don't allow players to affect the setting in any official way.
However, if you want to sit and natter IC about how your house caught fire and so on, that's fine. There's a distinction between your character just talking about stuff with other characters and something that affects the setting itself in some way.
In a town like Ford Keep, the homes and businesses are close together. A serious fire would threaten other parts of town and therefore become something that affected the setting...forcing other people to deal with a player's personal desires. Same reasoning behind people not being able to shake the tavern off its foundations or blow the roof or doors off. While the situations are different in effect, the principle remains the same.
If you want anything goes type stuff, you'll have to choose a setting other than the CRT.
Siani