Maybe they’re both more concerned with attacks from terrorist groups than from each other.
The analogy would be one guy telling a colleague that his fly is down before a client meeting. They both might want the same position but an unrecognized failure would make them both look bad.
My impression is that it's easier to attack than to defend or detect. That would make the country who doesn't attack a sucker. So treating it as an act of war isn't viable.
That's not "testing nukes in your own desert", that is "sneaking into someone's factories and planting bombs", if we're looking for an analogy.
And I'm surprised that this is openly admitted by the US, and tolerated by both sides, instead of being treated as an act of war.