Let's set politics aside and talk about risks.
Sometimes for some investors high bond yields are very compelling to invest. But unfortunately, higher yields also means higher risks. Countries that pay high yields means they are having difficulties on finding investors to buy their bonds. There are a lot of risks involved, but in Russian case the risks are clear. It's all about current geo-political uncertainties.
Lets compare some different 1 year bonds high to low: (real data from investing.com
United Kingdom 0.55%
United States 0.09%
By comparing the table above the investors are requesting Ukraine 20% for their money, from Russia 8.52% while they will pay Germany 0.08% to keep their money. Interest rates are linked to risks, and investors often are ready to pay someone just to keep their money safe (France and Germany on this case).
On the long run, if yields remain high it will become a burden to the country. A lot of tax payer money will go to paying interest. High yields will lead to deflation (the country will be forced to print more money) or even bankruptcy. It was not a long time ago since last Russian bankruptcy, only 15 years ago.
Of course it is not safe to buy Russian bonds. As a matter of fact, there is no safe bet. It's just different levels of risks. There is a golden rule to investing: 'If you want to make money you have to take risks'.