From the article: "You can mail a single postcard and it will only cost you $0.70 all-in, no strings attached." That appears to be the cost penalty for sending postcards from an API. Less than half of that is postage.

There's still a direct mail industry, but it's all about getting the big discounts available if you send in bulk and pre-sort everything. It's a form of spam; most of it is discarded.

Worse, people who still pay any attention to paper mail are likely to send you back a reply on paper or call you. Now you need a mail room, a data entry operation, and a call center.