Some lenders do consider the total amount of debt you owe in addition to the payment due. IBR is not a gaurenteed payment plan, it is subject to change as your income changes, and it can also lapse if you fail to submit the paperwork that's required. That situation carries some risk that someone with a lower total balance, or a larger percentage of their debt paid off does not have.
You may want to try applying to another CC company, they all have different standards. You might poke around the CC forums here to pick a company or two with cards that you like that have more forgiving standards.
