They have been. Through MOST of the member countries.
They have no leg to stand on in this suit because three countries is not MOST of the EU.
In general, as migrants were dispersed to EU countries willing to accept them....they left their designated country (the EU doesn’t track this or keep numbers). Chief reason? Ninety-percent of the EU members don’t pay enough to survive in this status. So these folks drift off pretty quickly to Germany or France. You make up a new fake ID and just show up....the Germans have to accept you.
The other little thing which I doubt that the EU wants to admit in court is the Schengen Agreement (all of the EU members signed to it) says that where you land, is where you must apply for a visa. So the bulk of these 160,000 refugees....landed mostly in Italy and Greece. By the treaty, they’d all have to stay in Italy or Greece. On this fact alone, a court would throw out the the EU lawsuit.