3 What greatly contributed to the realization of Our plan was that on being asked for your opinion, you welcomed Our proposal with great approval. As the time approached to make the idea a reality, We gave you the choice of location for this meeting. Most of you indicated that you would prefer to meet in Rome, especially since it would be easier for the majority of you to come here than to go to some distant American city on account of the difficulties of travel in your own country. We could only give our complete approval to this declaration of your opinions which was no light indication of your love for the Apostolic See. However, We are bothered that Our present circumstances do not allow Us to treat you with all the liberality and honor We would like when you stay in Rome.
Source: Quum Diuturnum (Vatican.va)