Well, they became opposites. If I understand it right, it's kinda just what happens when two shards settle a system. Preservation vs Ruin, Devotion vs Dominion, hell, even Cultivation and Honor were down this path before Odium came. I think Shards naturally polarize, so that they represent the two extremes of ideology. Ruin, despite being the god of Destruction first and foremost, eventluy came to represent all change on scadrial, despite some change clearly being Cultivations. Cultivation was starting to become something of a rulebreaker, while Honor grew more obsessed with rules. Devotion would reasonably become You Serving Others, while Dominion became Other serving you.
This Wob