You're in a room and you hear the distinct sound of the Apple Watch ringing, you check your watch or your phone, but its not yours. You notice others also checking their devices.
When everyone has the same ringtone, everyone is fooled. But the only ones who are fools are the Apple engineers who decided that no one should have a unique ringtone. The tech exists, but no one is allowed to have it. Maybe they spent all of their mental resources figuring out how to add stickers and animojis to the iPhone, and forgot about the basic functions of the Watch.