Anyone know why we still get these?

This afternoon as we're walking up to the house, I see both of the boys bend down and stare at something on our front porch...

Holden: "What is this?"
Me: "A phonebook."
Holden: "What's a phonebook?"
Me: "It's a paper way of finding phone numbers."
Holden: "Why do they use paper?"
Me: "I don't know."