How About a 17 Hour Training Day?

Athletes training for Olympic Distance Triathlons often train 2-3 times the distance they race. Runners who race 5K's often train 3-6 times the distance. Why is it that triatletes training for Ironman rarely approach the distance, much less double it? How about a 17 hour training day is a site developed to follow the progress of a team of athletes completing a study on the effects of such training.