Once the dragons were gone, why is there a central state at all? You can think of two reasons lords would submit to and enable a monarch: they’re forced to (by fire) or they benefit from central authority in some way. For the latter to work though, you’d think the Iron Throne would have to be projecting power outward from Westeros, bringing in land or plunder that would make submission to a king worth it. But it doesn’t, it just sits.