Why is the reverse phone number lookup a paid service?

I don’t understand why I get a phonebook with a ton of addresses and phone numbers for free on my front step, but trying to look the information up the other way is something that I have to pay for.

I seem to get a lot of prank phone calls, I think because my phone number is kind of an “easy” pattern on the dialpad. I got one last night at about 3am, and it scared me a little bit, and today they called again a few times, and also left me an odd voicemail. The number isn’t private… but I’d have to pay to find out who it is.

That makes no sense. If you have a name, but no number, you can freely obtain contact information. If someone contacts you, and you have contact info but no name… that costs money. Why?