Lag is the biggest issue by far, but it's still no excuse for the high % of 3's that go in for these guys. I'll be honest, I have to play off ball D a lot so that I can play help D because the lag is so bad I can't stay in front of my man w/ the ball. Also doesn't help that help D is broken as well. Contested shots go in at a ridiculous high rate in this game too.
So a combination of a lot of little things pile up and turn into 3 point barrages in the long run.