Milwaukee currently shooting 74% from two, which is just ridiculous. The Pacers' defense has not been good, but I also think it's been better than it might seem just from that number--based on ESPN's shot charts, the Bucks are 6-8 from two on shots outside the lane, most of which have been pretty well defended. Even with the shot-makers that the Bucks have, you wouldn't expect that to continue.
Of course, even with the most wide open threes, you also probably wouldn't expect the Pacers to stay over 50% from three in the second half, either.
Turner is a REALLY efficient player on offense but not great on defense even though he has all the tools. Siakam is better on defense inside and that addition helped but they still struggle. Carlisle has had great defensive teams in the past so I think it's a deal where he's coaching to the roster's strengths.