Russian organizations may receive euros as payment, which are still usable in Europe to buy things. This gives the EU a huge level of control over Russian spend

Russian organizations may receive euros as payment, which are still usable in Europe to buy things. This gives the EU a huge level of control over Russian spending in their markets; if they pay less, it's not like Russia can just exchange some rubles for eruos, they have to deliver products and services (which now cannot go to Putin's war effort).