PotD: Visa or MasterCard?

[Kalahari Inkantation]

the enormous disparity between these poll results (11:1 in favor of visa) and the american average (5:3 in favor of visa) is noteworthy

i wonder why the difference is so great

what is it that makes boyagers 5.5x more likely to end up with visa than mastercard, when the average distribution of cards in the us is only moderately skewed in visa's favor