The primary reason banks want to keep business accounts separate is because different laws apply to consumer accounts. For example, if you read the FCRA, you'll notice that it defines "consumer report" as pertaining only to credit "used primarily for personal, family, or household purposes." So, business cards aren't covered by the many consumer protections that consumer financial transactions receive. As long as you pay your bills on time and don't have any other billing disputes, you might not notice any issues. But, if push comes to shove and you need to enforce your rights under the FCRA, FCBA, or their implementing regulations, you might find out that the bank holds all the cards. So, the credit card issuers want to make sure they are complying with the relevant laws, and they also don't want to waive their beneficial position with respect to business accounts by allowing customers to charge personal expenses such that the customers could then claim that they should be covered under the more protective consumer laws.