Why Do You Care If It's Popular?

Today, as I was ringing up a family, the father pointed to one of the items they were getting and asked, "Which is more popular, this one or the blue one?"

Why did he care???? From what I saw, the daughter of the family picked out the item, so why does it matter which one is more popular? She liked this one.

The only time I'm even remotely ok with people asking what's popular is when they're buying a gift for someone they don't know. Then they're just playing the odds, hoping the person will also like the item. But if you're buying something for someone you know (or for yourself!), popularity is irrelevant.