In this past Monday's edition of "Merger Monday", investment/corporate watchers were blindsided by $82 billion in proposed deals.
I guess it depends on the situation, but I wonder if corp. comms pros would rather have a distracted press or a slow news day when announcing a big acquisition. Plenty of column inches vs. less prying eyes. As with everything, it's a trade-off.
At least one of these deals was hostile; I assume they have a different opinion on this matter than a merger of friends.