While the hex bar, or "trap bar", is very popular nowadays, we do NOT utilize it for the deadlift for a couple reasons:
1) There's a reason it's popular
People tend to like what they're good at, and EVERYONE is good at the hex bar. We've had athletes that pull 405 with a straight bar, go to college and use the hex bar for easy pulls of 600 +. Why? Because the leverage point more closely mimics a deadlift off high pins in a rack, than a deadlift off the floor. For those who straight bar deadlift (with an actual FLAT back), they know well that the hardest part of the lift is breaking the bar off the floor. The hex bar however, positions the weight at the side of the athlete not in front, allowing an easier starting leverage point. There's another reason though that there's such a discrepancy between the bars, and that leads us to the second point:
2)It defeats the main purpose of the deadlift
The reason why the deadlift is so effective for athletes is it allows you to build tremendous force production using your POSTERIOR CHAIN. With the sumo deadlift, an athlete must pull with a vertical shin to be effective, recruiting massive force out of the hips, hamstrings, glutes, lower back, and upper back. The hex bar however, puts the load at the side of the athlete not in front, and permits athletes to slide their knees forward into a sloppy position that DE-EMPHASIZES posterior chain development. The vast majority of athletes are very weak in their posterior chain, and desperately need to develop it for optimal sprint speed, jumping ability, overall explosiveness, and power in the hips. Unfortunately though most try to completely avoid it by using a regimen of dumbbell presses (chest), curls, and hex bar deadlifts, leaving them with a physique that LOOKS strong, but PLAYS slow, the classic "look like Tarzan, play like Jane". The athletes that develop thick hamstrings and glutes, strong lower back and hips, are the ones you wouldn't want to get into a fight with, and that also dominate on the field. A vertical shin, straight bar sumo deadlift forces the athlete to develop those weak points, and has MUCH greater translation to the field.