The value of cryptocurrency is usually tied to the price. The price is determined at exchanges. Russia however can’t use foreign exchanges as the accounts there normally require identification (some offer pseudonymous crypto to crypto swaps) as the exchanges don’t accept Russians, and if you want to convert crypto to a currency, you need a bank account calling in that currency, which is not happening. If the exchanges even transferred money to those as they’d lose their license.
The value of cryptocurrency is much less than what you see on CMC etc. if you can’t actually convert it to those currencies. Which is the main issue.
Add to this that most crypto currencies can be traced and having transacted with known Russian problematic accounts - even via proxies - taints your wallet, making it hard to impossible to buy and sell on exchanges later down the line.