Because merchant account is a contract with you and the bank. You get an individual merchant account that If any card provider doesn't like you, they can ban you. Stripe, you're using their merchant account. If banks ban that merchant account, they ban all stripe customers. Key difference in risk for your payment processor. I have had banks ban my merchant account but my payment processor didn't care.
Due diligence, lol. In fact, the world is just a huge mess, and you have to have backup plans for all the important things in your business, or not care for downtime.