the scales of the games on a different scale. RDR2 had most of the map with nature, without any details needed. Just code some trees, some snow, do a small city, some villages with the same type of structure and there you go, you have the map. CD Red had to actually build a city.
Regarding quests and story, I won't even get to that, since I finished 10x worse games than RDR2, but I couldn't finish that one.