Bosh isn't drawing any of his defenders to the three-point line because they are not going to defend Bosh's three-point attempts. Nobody isn't respecting Bosh's three-point shot. Opposing teams defensive would rather leave Bosh open from the long-range so that they can close the lane. There's isn't going to be any spacing to penetrate the lane when the defense refused to contest a long-range shot. Did you forgot how Duncan had disrespectfully left Bosh by himself in the three-point line and not moved from his position to prevent Wade and Bron from penetrating the lane?
Any team with discipline in defensive isn't going to run out of the lane to contest Bosh's three-point attempts.
Bosh needs to move closer within his range to accurately shoot his mid-range shot and to attack the shot-blockers. If he can do that consistently, then our offense will run much better, because it will draw front-court players on to him, which will open the lane for Wade and Dragic.
Also, Nowitzki is a respectable volume 3pt. shooter in the league, and in comparison to Bosh, most of his three-point shots has been contested. Most teams are not going to sag off him from the three-point line. They wouldn't dare leave him open on the three-point line in every possession.
@ Bosh being an accurate three-point shooter compare to Nowitzki. Bosh shot the three at 37% percent last season, but he had played 44 games and that was his career high. His three-point shooting rate probably would have fell off if he had play more than 70+ games. In this season, Bosh shooting the threes at 39% rate, but that's in ten games. I doubt he will continue to shoot from downtown at this rate as the season progress. Nowitzki has taken more three-points attempts at a volume rate through the course of his career and efficiently shot the three at 38%.
Bosh is a great player when he wants to be, but he will never be a great volume three-point shooter like Nowitzki.