The sanctions on Russian oil weren’t intended to keep Russian oil out of the market. They were designed to prevent Russia from profiting richly from its oil sales.

Removal of all Russian fossil fuels would have had a dramatic impact on the world markets because the supply disappearing overnight driving up the cost of non-Russian supplies. The way the sanctions worked made it so that Russia could only sell its oil for cheap to the markets are still supplied, yet they can’t make huge profits from it because there are so few that would buy it directly.