Even for non-commodities, customer contact information can be invaluable. Often would-be repeat customers just forget you exist, but if reminded about you they

Even for non-commodities, customer contact information can be invaluable. Often would-be repeat customers just forget you exist, but if reminded about you they would happily continue to buy. The same reasoning for websites periodically sending their users emails is at work here. Remember how Facebook used to send email notifications that you've received a new Facebook message, but wouldn't tell you the content of that message in the email? "Hey, we have more goodies back here - come visit again."