I would imagine it might just be because Russia has those same missiles pointed at major European cities?
Using rubles for contract settlement doesnt mean they are trying to make the ruble a reserve currency. They're basically just forcing anyone buying their oil to backstop their currency thus its not going to lose much more value due to sanctions. Timing is not in Russia's favor. The cold ass winter is almost over so the high demand for gas/oil is no where near its peak. IF this shyt lasts into next winter, EU will have to replace Russian production or Russia will have an enormous amount of leverage while EU freezes.