Aight sick, so why invite anyone? We're all NATO in the EU, right? Just have Macron, Antonio Costa, Ursula von der Leyen and Mark Rutte in the room.
Poland is officially considered Central Europe, but sure, why play semantics? Let's call it Eastern Europe. This would be an even better reason to invite all other Eastern Europe reps. Why just invite one, right?
As far as I can surmise from the article, no. No one else was even invited.

Did you just call the meeting where EU decides their approach to the conflict in Ukraine with waning American support a fucking brainstorming session? This is not fantasy football. People's lives are at stake, both in Ukraine and otherwise. If the world wants for the EU to show a united front, then why not have a fucking summit, instead of cherry-picking?
Adding to my answer, it is just as I said. The reps of only those 8 countries were invited, plus Ursula von der Leyen, Antonio Costa and Mark Rutte. This is not an EU summit. That's the entire problem.