Direct mail can walk right past the door and on to the dining room table. You can't get those kinds of results from digital mail. A strong, well designed mail piece meets the train of thought of the recipient. It may sit on their counter, waiting to be visited again, or placed on the refrigerator for further use (in the case of coupons.)
Think about the premise of direct marketing. You are sending out an offer to potential customers to try and entice them to buy your service or product. It’s not a general advertisement like a billboard on the side of the road. It is an advertisement sent directly to a person, usually based on demographics or past interest.