The logic is that, if Russians want to hold wealth in another currency, it would be difficult, if it is all about just paying someone in another nation, then they could do it. The difference is that, if you want to pay me, someone who is not Russian, you can and Russia will be losing money there, whereas they will get something from me.
But, if you are a Russian wealthy person, then you can't just use crypto to take it out and turn it into another fiat. You can't just buy bitcoin with ruble, then turn that bitcoin into dollar and put that dollar into your bank account. Bank will notify the government and government will freeze your account and your money would be gone.
And it's not just about that. Even if this could be done with less difficulty, it is still the path of a minority of the Russian population. It will not save the country from sanctions, although it may save some people. Russia is a country that exploits natural resources. It is vital for them to sell them. Without this permission, they will default. And even if there are not enough rational reasons for this and there are certain ways to circumvent the bans, the panic that has already gripped the population will end the case.