You got me
Personally, I think our DBs don't know how to use the rules to their advantage. They jam within 5 yards, but don't know how to back off once the QB releases the ball.
They also have terrible technique tracking the football. They play the body, instead of the ball, which is why our DB clumsily bump receivers downfield. The body is deceptive, but not the hands. The hands always tell you where the ball is, and gives you a pretty good idea when it's arriving.