While i agree with your logic, i managed to find some BTC seller who accept RUB at HoldHodl[1]. But obviously the rate isn't fair. At time of writing the post, those seller charge 4-30% higher.
That's not unexpected, by far. Keep in mind that any seller risks that until the point he will spend those RUR they will probably worth much less than at the moment of trade.
And obviously the sellers also try to profit greatly...