0% intro APR offers are somewhat predatory in that they rely on a large portion of people keeping a balance after the intro period in order to be offered, or at least building a relationship with other financial products. It wouldn't surprise me that they would reject someone in the high 700s, they might have been looking more for people in the low to mid 600s.

There's also a lot of reasons one might be rejected for a credit line that have nothing to do with credit score. Some lenders have specific policies in addition to credit score, like Chase's 5/24 rule. Some are also just looking for "relationships" and won't offer you their best products unless you have a bank account with them, etc.