Aside from exorbitant fees and maintenance charges, the information harvested from credit card applications alone is worth money to the company as they can sell that specific demographic/personal info, often with names, addresses, phone numbers, email addresses and birthdate conveniently attached, to other "partners" for targeted advertising, purchase habit tracking and other nefarious reasons. Yes, that is still a thing.
Read all the fine print and you'll see that you can opt-out of that sales program, usually about 3-4 months after they have had ample chance to sell it and even after receiving written notice of opt-out you'll find no specific guarantee that you won't still receive targeted advertising beyond that point. As they say about posts on The Internets: Once the information is out there, it's out there!
It's like a paper-trail version of a computer "cookie" that can be used to track your every move. And it amounts to extra, easy, side income for the business.