Because if poeple would sell their rubles for Bitcoin as the ruble becomes worthless, it means somebody is selling those bitcoins for rubles, right?
That's why I said the options are limited. The available options are most probably in-country, either face to face, either with the account at the same bank.
Don't rule out completely the option that some Russians may need to sell BTC for fiat (RUR, USD, EUR) for their daily spending.