"those countries that previously used or stockpiled NATO-issue firearms and the 7.62×51mm rounds,” suggested Alexey Leonkov of ‘Arsenal Otechestva
Makes sense, in the same way that producing magazine adapters to take on STANAG magazines does.
Turkey, India, Pakistan and other countries (particularly those with mountainous terrain it seems) have all continued their interest in 7.62x51 rifles for standard issue, not having to replace or sell cheaply the entire stock of ammo does of course make sense as well.
I have to admit that Russia has ridden out the urge to change calibers frequently. 7.62x54R with 128 years of service is the longest serving cartridge ever. Goodness knows how much they must have stockpiled.