Because Russian banks need to be capable of transacting with American banks and directly receiving money that is Ransom Payment related is a bad business decision.
So you're saying sending money to a bitcoin address would help obscure the identity of the receiver?
No I'm saying a Russian bank probably doesn't look past the deposit. But if the deposit comes from America then an American bank will ask for it back when the US govt tells it to and then the bank will do so because it's good business. So I would imagine most ransomware gangs just keep the money in bitcoin and only pull out what they need to when they need to.