Why am I being denied from these banks?

Hello!

I have applied to AMEX for the BCP and Citi Bank for CCC (I applied to this after getting denied by AMEX). Both said I have a limited credit history.

For context, I have one credit card (Savor from Capital One) for about 2 years now. Paying on time each monthly payment. I also have been paying for my car, under my name for almost a year now, on time. My credit is 726 under FICO.

Is my credit history that limited to not get approved?

Thank you!