Because Coda edges and flaws have greater impact on the character than Icon edges and flaws. As a result, Coda got rid of all the purely-roleplaying edges and flaws (i.e., those with little or no mechanical effect on gameplay).
So, minor roleplaying effects like Oath (Hippocratic) were dropped in favor of making them purely roleplaying effects with no point/pick value.
I'm sure Don or Doug can explain it better than I (since it was from them that I heard the explanation in the first place
).
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz