Saying “We heard something in that multi square mile area that may be worth looking into” is way different than “We know exactly where and what it was”
And how quickly they could definitively identify what the sound was and where can play a big role in identifying capabilities of the systems at play and the how advanced they are
And of course knowing capabilities is a key part in developing systems to circumvent such systems
Basically what I’m trying to say in entirely too many words is that specifics matter a lot, especially to the military. And specifically knowing what someone is capable of can be used as a way of getting around it or using their own systems against them. Especially so that you know you’re not investing in systems research that is already defeated by anothers systems.
How quickly they process the information, how accuratly they could determine the source, and how accuratly they could determine the location would all be fairly sensitive information.
Basically what I’m saying is that if they announced right after it happened that “Hey guys that sub imploded at X depth and the debris field will be at Y location because we heard a pressure vessel of the correct size crush followed by the sound of something of roughly the correct mass crashing into the sea floor.” Then everyone would know how capable our equipment is.
Basically announcing it days later gives a conclusion to the questions of what happened and also will likely keep others from meeting a similar fate. Not to mention the benefit of telling other countries that “Yes we can and will find out about what goes on underwater, just how quickly is more of a mystery… For you.”