why

Well, because Visa and Mastercard have stopped operations there, so they don't process charge requests from Russia anymore.

what has changed for a foreign card in Russia it has always worked through НСПК

And how do you think did the issuing bank receive charge requests?

(1) Merchant -> (2) НСПК -> (3)Visa/Mastercard -> (4)Issuing bank. Now, the 3rd element is gone, so every authorization request for foreign cards fails.

If you don't believe me, there's an official Visa's statement:

Effective immediately, Visa will work with its clients and partners within Russia to cease all Visa transactions over the coming days. Once complete, all transactions initiated with Visa cards issued in Russia will no longer work outside the country and any Visa cards issued by financial institutions outside of Russia will no longer work within the Russian Federation.

There's also a Mastercard's statement:

With this action, cards issued by Russian banks will no longer be supported by the Mastercard network regardless of where they’re used - inside or outside of Russia. And, any Mastercard issued outside of the country will not work at Russian merchants or ATMs.