the companies listed there get their mailing lists from the USPS. they buy bulk mailing permits and address database from the USPS. commercial printers hired by those marketing firms deliver junk mail by the pallets to USPS processing centers which inkjet mailing labels before sending them out. if you think opting out will remove you from the junk mail list then you are wrong. not all direct marketers buy up to date database with the most current list of opt out consumers.
I guess you can't read. "We do not sell or rent your personal information to outside parties."