I can see how it would come in handy for an active family.
Sure, they may have only two kids, but when they go places, kids bring friends. I know whenever we went camping or backpacking, or to Disneyland or Magic Mountain while I was growing up, each kid in my family brought a friend along.
We also car pooled kids to events.
And on the subject of camping or traveling, have you ever tried to fit everything you need for a family of four in a car or small SUV? You can't, you need a trailer or rooftop box.
My parents got a full size van back then (about the biggest thing you could get in the 70s), and it STILL was too small for us. My dad had to get a trailer AND a rooftop box for when we went camping.
All I'm saying is, unless you know these people intimately, you cannot know if they really need the vehicle or not... nor is it up to you to determine that.
When you see the woman driving a large SUV alone, how the fsck do you know why she's alone? Ever occur to you that she may have just dropped the kids off someplace, or is on her way back to get them?
In fact, A parent will be alone in their family vehicle a majority of the time. Does this mean they have to buy a smaller vehicle because it offends you to see them driving it alone?