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I wonder if it’s because the iPad is more often a family device, whereas no one could argue that for the iPhone.

I understand there would be ways to work around that, but I can see that as an argument.
I don’t know, but it’s always felt like a big oversight that it’s not been included on the iPad from Day 1. Both the iPad and the Mac are generally better devices for planning things ahead, like adding clinic appointments, scheduling workouts, diet and meal planning, etc.
 
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