3 days is a pretty long time unless the damage is catastrophic and very broad based. Extended preparations come with an overhead cost that must be offset by the benefit.

Denmark specifically is not a populous country. You could probably keep the entire country fed with just the capacity of e.g. the US military airlift capability, which has been used in these situations. The emergency reserves mostly only need to exist until supply chains are established. It is a balancing act.

> US military airlift capability

That'll cost them Greenland.