When the losses/deaths that result from practice exercises exceed those from the actual events practised for, you do have to wonder why they continue to practice. The RN submarine service used to practice escapes from submerged submarines, using emergency breathing apparatus in a 100 foot high water-filled tower at Portsmouth. They lost 1 or 2 submariners each year, either killed or permanently disabled, until they worked out that the last death from a RN submarine was in the 1950's, and they had lost more men practicing since then than had died in the last event.
So they stopped practicing in the tower, and worked out another way of getting the men out, from a greater depth than was possible before, by using a rescue sub.