Oil price is set by supply and demand. Demand is still unfortunatly slowly growing. So if you cut supply, by for example stopping Russian oil exports, you then increase the oil price. The bad part in that is that it probably leads to Russia being able to somehow export oil around those sanctions(like via land to China for example) and actually make more money with it then with sanctions applied. This is made worse by Europe being oil importers, so a high oil price hurts Europe.

Right now a number of things come together. Trump caused a recession in the US(lower oil demand), EVs are growing in sales(lower oil demand), Venezuela Maduro stuff(higher oil supply), OPEC increases oil production(higher oil supply), Trump makes it easier to frack in the US(higher oil supply) and so forth. The only thing increasing the oil price right now, is a potential invasion of Iran. However even that does not seem that likely. In other words cutting off Russian oil supply, is currently possible.

Then Trump seized a Russian tanker and nothing happened and Greenland happened. Therefore Europe knows the risk of doing it are lower then thought and they have to take risks to make sure they do not depend on the US, if Russia starts a war against the EU directly.

Oh and Russia looks weak right now. The economy has some serious problems, so this is likely to really hurt.