A few years ago 1 Ruble = 0.015 USD this was pretty consistent for a while. Now 1 Ruble = 0.010 USD this has fluctuated pretty wildly.
The fluctuation is far more important than the actual number. Nobody cares if 1 Ruble = $1 or $1000 as long as you can rely on it to be that next week and next year. But the fact that you have no idea how far down (or up) it will go means that people aren’t going to want to rely on holding any currency in Russia.