The instincts you have about privacy today are inappropriate for back then. It's hard to get to your mind around the difference sending an email, or making a phone call, or sending an SMS to anyone in the world being nearly free makes.
Back then in most countries even a local phone call cost a couple of dollars in today's money. Interstate and international phone calls had background 30 second beeps to remind you dollars were being poured down the phone line.
The effect of spam is obvious - there wasn't any. But you probably aren't thinking about the other end of the scale - what was an upcoming phone call worth to you? The answer to that is almost unimaginable in today's world - receiving a random international phone call is almost certainly worth the interruption many times over. That meant having your name, address and phone number published in a directory was definitely worth it. It was worth it to the phone company too, of course, because it increased the usage their network. So they provided the listing for free. It was a win, win for everyone.
To get a feel for how much it's changed consider the yellow pages. Businesses paid huge sums to the phone companies to get their phone numbers listed in other places in addition to the free one. The value of every phone call they got made it worth the money. Now I struggle to get to find the the phone numbers of many companies. It seems they go out of their way to hide it. That's the difference the price of a phone call feeling to zero makes.
