As I understand it it's not so much the labelling requirements per se, but rather that the FDA needs to approve the formula, including the label, and that takes times. For example the FDA probably wants to test that the nutritional content on the label matches what's actually in the product, or that it's not adulterated. This is fairly reasonable under normal circumstances IMO.

Some other requirements (like not having enough linoleic acid or iron) are perhaps more problematic than just the labels, and allowing formula which doesn't quite meet the requirements is a kind of unfair competition (that they happen to be imported from the EU is not really important as such).