The approach to FFX was very very different to that of FF7 as we all know, so going by that basis, you have to think that in X, these people have learned to COPE with Sin, they have no choice,they must live their rotten lives as they wish, but Sin will always be looming over them. Some may decide to be scared, but most in FFX chose to live their lives like normal cos..hell, they can't do a dam thing about it.
And also to keep things short, I found when playing the game, all the spirits and shit,they were pretty sad tbh, so many dead.