Maybe we can frame the question more to the point: “Why was there no international pandemic preparedness plan by the Holy See to ensure that the sacraments are administered effectively to everyone during a pandemic?”
That addresses the “problem” now that we have lost regular access to the sacraments unless in imminent danger of death. It also presents the obvious difficulty: the serious danger to the clergy.
I’m not sure what further aim for a global pandemic plan would be necessary.
A major difficulty now is the interaction of canon law and secular law, both common and civil. That’s a complicated thing. It would seem almost impossible to publish some definite international guidelines in advance of a situation that would unfold in innumerable unforeseen ways depending on the nature of the disease that causes the pandemic, the secular laws in place where it affects people and the response of the various governments.
Even now, bishops disagree on whether the measures taken, in obedience to secular laws, actually violate canon laws. And there is tension between the heroic ideal of continuing to minister the sacraments despite the risk to health and the practical requirements of the clergy. A pope might have put in place some international policy to close churches; aside from the complexity noted that would be effectively discouraging heroic virtue.