I think ot has to do with how hegemonic the status quo asumptions about the world are. For example japanise ligth novels and anime are generaly also like this. The protagonists simp for some monarch or some already exsisting structure. Contrast that to chinise wuxia novels where the protagonists usually remake the world as they see fit. I think this means the chinise audiences are corrently seeing their country being built up and so recognise that improvments can always be made and so change is good. while western audiences have been condotioned to beleve liveralism is the end of history and thus the status quo needs to be preserved (even if its a monarchy in a tantasy world)

As other posters have mentioned older turn of the century fantasy and science fiction involved more positive changes. There was after all significant technological progress and audiences could imagine improvments in society. So while many campbellian heroes are reactionaries in their values they all have their own ideas about how to change society. They are creative.