If I was being uncharitable I would suggest it's because of recent incidents meaning blizzard didn't want to court controversy by having both female aspects aligned with a healing spec, that and Alexstrasza is the box character so they want to associate her with dps since more people play dps.
More charitably, blizzard having been kicking around the idea of a healing time mage for years and they thought evoker was the time to pull the trigger.
Tonight for me is a special day. I want to go outside of the house of the girl I like with a gasoline barrel and write her name on the road and set it on fire and tell her to get out too see it (is this illegal)?
Some red abilities damage and heal depending on target. Unsure on green, but green probably shouldn't do any damage period. Red can go either way thematically but green historically has been more associated with healing.
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You're overthinking this.
There is a pretty strong healing component in Red spells.