Part of the reason Oz is such an ass is because he's afraid if he were openly sentimental about things one of his family members would write poetry about him.

After that came up in thread, I headcanon that Lowri Dempsey wrote some poetry just before/after he was born regarding her feelings about motherhood, baby Oz, etc etc, and that he read those when he was six or seven as an introduction to literary themes (in my heart all the Dempsey children were taught about metaphors and allegories and things shortly after they learned to read, as a matter of course) and felt really weird about it and that's when he started being more reserved about how he really feels.