Because it would slow the bow down a lot on a cam-limb bow and put even more stress on the hinge due to weight. A shoot thru system is not as big a PITA as some say it is; it just takes getting used to like anything else. Martin still manufactures those systems for those that want it, and many do because it relives the strain and cam lean on the cams. Oneida gets around it by using the cams above and below the sight window, Darton solves the cam lean problems as best they can with their harness/yoke system on their new bows.