why are ralph and jack soreadyto except the presents of the beast?

I think the mass psychology, no matter how bizarre, rubs off on them as well. Certainly Ralph has his reservations even when the twins claim to have seen it. Jack figures out early on that believing in the beast works to his advantage. Jack learns how to play upon the boys' fears and offer his "protection". He has none to offer but perceptions are all that matters on this island.