This is a great question because the answer to this is very interesting. 
This is happening because Zelensky has, for a second, entertained the idea that he can go at this war w/out the US and with the help of EU.
If such an enterprise succeeds, the repercussions are profound - the global order shifts. US as an empire becomes irrelevant. Empires can bear loss of territory, but not irrelevance.
So Ukr and EU must obey whoever sits on the throne in DC, if that can't be ensured nothing matters.
The "threat of a good example" applies to the EU too.

Interesting perspective on the potential shift in global order. Zelensky's actions could indeed have far-reaching consequences, highlighting the delicate balance of power on the world stage. It will be intriguing to see how this situation unfolds and whether it will impact the dynamics between nations.