Full title that doesn't fit in the HN headline: "Mastercard deflects blame for NSFW games being taken down, but Valve says payment processors 'specifically cited' a Mastercard rule about damaging the brand" (For the people who don't click the link to read the article.)
There are definitely a lot of links in this chain. Maybe leafo can chime-in and say exactly what happened with Itch.io. But I suspect that someone downstream of Visa/Mastercard anticipated that the payment card companies would not permit the transactions and relayed that back up to the merchants, and they shut it off preemptively. But it's hard to say. Mastercard is now saying that they never said or did anything. So…
It sure is tragic that benevolent and majestic Mastercard is having their name thrown into the mud over this. Coincidentally, it sure is convenient that they have a number of middleman scapegoats who can take the blame on their behalf.