Yes, Mastercard is almost as available as Visa, but Visa is still more popular. I still somewhat have my 1980’s anti-Mastercard bias, so them going with MasterCard initially rubbed me wrong (I even dislike their logo, lol). It’s possible it was a Goldman Sachs decision, or maybe Mastercard gave Apple more incentives to put them on the Apple customer map. Like say, the barrier to entry for Visa Signature was more difficult as an upgrade path, but Mastercard might be willing to make concessions. All speculation of course. But it seems to me, if Apple was behind the decision, then there were incentives.