Defensive effort across the board has been better this year. Even poor defenders like Beasley and THJ are at least giving effort on most plays.
Pistons have the 14th ranked defense in the league. If you would have told someone that before the season started, they'd have said you were crazy, especially after the Pistons brought in mostly shooters and weak defenders to shore up the offensive spacing.
Coaching matters. JB isn't elite, but his teams play defense, his rotations usually make sense, he works the refs, uses his challenges, and I've seen some nice in-game adjustments here and there. Night and day from Monty "The Terrorist" Williams.