Maybe because they know that if they assemble and cooperate for just three pictures, we'll get one good one, and I will let them go back to what they were doing. It doesn't have to be perfect; no family is perfect. We don't all have to have a matching outfit, either. Or fuss over our hair. Or give a "SupaStar smile". We didn't even have to travel any further than our own home. We just have to be our natural selves - that's the beauty of the family photo.
It wouldn't have had anything to do with the act that I texted them about it the day before, would it?