You can try to argue this down and reason about it all you want, but it's still a bad default regardless of how it's presented to the user. It's also bad design because it conflicts with similar defaults such as the shortcut to open the camera (press power button twice), silencing an incoming call (press once), etc. People may also press multiple times when the phone seems unresponsive.
You'd expect the resurgence of bad defaults to be motivated by marketing or something, but this one is just outright stupidity.
There's a part of me that is fairly convinced this was added as an afterthought after much internal whining by someone at google with a checklist insisting that android must support some easily accessible emergency feature. This was then deliberately chosen to make the feature look bad, and the users are victims of office politics.