What do payment processors have to gain by shunning Steam?

The current situation with Steam, itch.io and some other digital distribution platforms, and their payment processors, is very confusing.

VISA and Mastercard both have made public statements that they don't police content, as long as it's legal, and that they have not contacted Steam or any other platform in this regard, nor made any demands.

Valve also made an announcement through an online gaming journal interview that was superficially clear but still somehow extremely vague, which appeared to answer all the questions but in my opinion ended up not answering any.

Well, at least one thing Valve made very clear in that response, and that was that, indeed, they have had no direct contact to or from Mastercard nor VISA. Instead, apparently there's a very complicated semi-hidden network of intermediate payment processors and banks that stand between those companies and Valve, and apparently some of those had made those demands (although Valve's statement didn't give a single name, or specify what the exact demand were) and hinted that Mastercard had directly ordered those intermediates to do so (without giving any proof).

It's all very confusing.

To stir the confusion even further, suddenly PayPal decided to stop serving Steam, except for five of the most common currencies, and they, too gave a somewhat vague allusion to some banks having made that kind of demand or something. In other words, it's not PayPal themselves who are directly shunning Steam, but some of the banks or payment processor intermediates who are forcing them to? I'm not sure if PayPal, or anybody, has even named those banks.

It's all really confusing. 

This raises a quite relevant question: Why?

Why do some random banks that nobody even knows as being intermediates between VISA, Mastercard and Steam care about what kind of games Steam is selling? What exactly are they gaining from suddenly creating all this controversy?

The reputation of VISA, Mastercard, PayPal, and those intermediates, went down the gutter overnight, and their helpdesk phone lines have been flooded by angry customers. In other words, their reputation took a huge hit, and they are currently the center of a huge controversy that has got worldwide attention even in the mainstream press.

So the question is: What's the upside, from their perspective? What exactly do they have to gain that balances out the negative reputation? Why are they doing this?

After all, the apparent reason they are doing this is completely asinine: Even if Steam is selling some naughty games that some people find objectionable, who in their right mind would start blaming some random bank that nobody even knows is the intermediate between Mastercard and Steam? These random effectively-anonymous banks and intermediate processors are taking a hit to their reputation in order to avoid their reputation being tarnished by... pretty much nobody? Who even knew that these banks were involved in the transactions between the user and Steam?

So I'm left completely perplexed: Why? What exactly do they have to gain from this? What's the long term plan? What's the upside?

Valve claimed that Mastercard (and possibly VISA) directly ordered the intermediates to do this. Mastercard has denied this. One has to wonder that if Mastercard is completely innocent and uninvolved in the entire thing, why don't they do something about it? Why don't they tell the banks "stop doing this shit in our name, you are ruining our reputation! If you want to do it, do it in your own name, not ours!"

The total silence and inactivity from part of Mastercard and VISA gives some credibility to the claim that they are, indeed, behind the entire thing, and that they have commanded their intermediate banks to do this, rather than getting directly involved.

And once again: Why? What do Mastercard and VISA have to gain from this? What's the upside? What's the long term goal? Take a huge hit to their reputation in exchange for... what, exactly?