Shabbos 55 – שבת נה

Hashem said the tzaddikim of Yerushalayim are not to be held accountable since their reproof would not have been heeded to.  Why is this different than the typical case of reproof, where one who refrains from doing so is held accountable for the sins committed, although (from Hashem’s perspective) obviously the sin was going to happen in any case?