Because of Resto Druids. Storm Bolt isn’t available to healers cuz it’s a Warrior ability.
And before you say “but they can make it work differently for each spec”. Oh sure, they COULD, but they won’t. After all, they’re nerfing Swiftmend to be worse for everybody except Resto in Shadowlands, too…
The entirety of the Druid class is designed first and foremost around the assumption that everybody is a Resto Druid. Hence things like Heart of the Wild as a “feature” in Shadowlands, which is fantastic for Resto Druid, ok for Balance, not so good for anyone else.