Putting it on the same day minimizes the traffic, volunteer and cops issues, complicates race day, means organizers are more spread and creates some confusion amongst athletes. Hopefully it won't lead to longer lines at 70.3 packet pick-up etc. since those are already often pretty bad. Hopefully the 5i50 will do packet pickup on race day while the 70.3 is starting or somesuch.
race coordinator Bill Burke said "the plan is to have the 70.3 start approximately 90 minutes before the 5150 to allow for the 70.3 leaders to come in before the 5150 winners." [Read more here on nola.com]. Burke also said more races will be adopting this format of both races on the same day.