If it is a political and subjective decision as you say, then they have to balance the benefits of the declaration against the risk of the counter-narrative overwhelming it. Too early and even more people would dismiss the problem than are doing so now. And there's no "we said 'pandemic' before, well, it's 'really a pandemic' now" label that can be used.

And leaving aside the immediate difficulties...let's save this kind of retrospective criticism for after, when we're closer to being out of the woods.

If you have prospective criticism -- what should be done now and going forwards -- that would be worthwhile.