That is a good question.
What is happening is it's not being produced. Russia does not have much possibility of storing gas at home, so Gazprom production has fallen. Gazprom is also beaten by the independent produced Novatek that is much more efficient. Gazprom's share of the total domestic market has fallen from something like.... Total Russian gas production has fallen from something like 85% to 65% over the last half a decade. Those are just approximate numbers.