Employees who use their personal card for work expenses, and may be unable to pay if their employer fails to reimburse. Also, there is a difference in the consumer protections provided by personal and business accounts. It could be that American Express is seeing disputes for commercial disagreements on personal cards, and it would be easier for them to disclaim responsibility if the transactions were made on a business card.

It would be interesting to see if this language appears only on Delta co-branded cards, or more broadly.