The enemy of the (perceived) enemy's economy. There is a war in Europe, and the EU and the USA are mostly involved economically. Causing economic damage to the financiers of the enemy is a standard Cold War pattern. Oil-embargo warfare is a double-edged sword: while it hits the EU hard, it also causes pain for Russia. This is most likely one in a series of low-hanging-fruit attacks intended to cause economic damage to Ukraine's financiers.