Grusch testified that UAP are observed everywhere the Navy operates across the globe. Additionally, allied and other military forces also admit the presence of UAP activity.
If we discovered alien planets filled with different "countries" and had some constraints on the time we could spend visiting each one for observation, wouldn't we likely choose the most militarily and economically powerful one to focus on? It wouldn't be 100% but it's plausible that it would be the main subject.