Because the alignment, or the potential for such, was not apparent [to anyone at the table] when the DoW started. You don’t ever see huge shifts in perspective during a DoW? I find those the beauty and hallmark of the DoW mechanics, those “o-o-o-okay” moments where everyone at the table realizes the entire tone and direction of the campaign has noticeably changed even before the DoW ends.
P.S. What I’m talking about is probably better described as baiting. Keep in mind I tend to have a ‘good for the goose, good for the gander’ attitude, when GMing I’m happy to see players baiting me on NPC BITs.