When you take the economic activity of one currency that has higher rates, you also need to accept the devaluation of that currency, since the higher rate is associated with a certain element of inflation. When you then translate those dollars to a lower interest rate currency, you’d lose the premium of the return. 7% there, compared to 1% here, would be gobbled up by currency deterioration. There is no free lunch, interest rates/currency are like a nearly perfect functioning clock. Trust me, if it was that easy...those of us in Finance would cash in on that all day long.
Not sure if this site is reliable, but https://tradingeconomics.com/united-states/inflation-cpi puts USD inflation at 2.5% in Feb 2020, while https://tradingeconomics.com/russia/inflation-cpi shows RUB at 2.4% and dropping for the same period.
Indeed, I read the CBR (Central Bank of Russia) reports often, and inflation has been under control for quite some time now. My understanding is that the high rates are being maintained, and slowly decreased, to prevent the economy from heating up too quickly.
Another consideration is that in recent history (after they allowed it to free-float in 2014), the USD-RUB rate has fluctuated quite a but. The last couple years have seen it trade in a pretty narrow band though.
My strategy to is keep a non-trivial amount of money in Rubles, but only that money that I plan to spend in Rubles anyway (I spend a good amount of time in Russia), this way I don't have to worry about losing any gains in the FX rate.