When they-them-those know who you are, knowledge of the full attack surface is the better way to compromise because it leaves the first step to compromise uncompromising-appearing. (The attack surface is broader than people generally consider, as it should include over-the-shoulder attacks, XKCD's wrench attack, etc.)

The success of such tactics can more easily be understood by even looking through the many, many comments right in this thread telling us Signal protects metadata because usernames are now a feature - guys, Signal has the metadata as the *services* are what is the topic of discussion here, not other users.