Does anyone who knows transaction processors well explain why AXP has a significantly lower P/E than V and MA?

I am researching some of these payment processors and came across something strange. Using last year's free cash flow, Visa has a P/E ~29. Mastercard ~37, and Amex ~9. Why is there such a significant drop off?

The only thing that comes to mind is it could be due to their debt load. Although they do generate a ton of free cash. What do I know lol.

While you're here, what are your thoughts on the 3 companies?