Surely there are ways to get rid of it without the transition being so traumatic. For example, the change could be announced a few years prior, and the downtime could go down by an hour per year.
The change would be traumatic no matter how long they are given to plan for it.
Oh, here's another reason I forgot to mention: You can capture huge profits by exploiting the opening and closing few seconds of the market. A huge portion of all daily trades happen within the first few and last few seconds of the day. So there's a financial incentive to leave things as they are.
>the downtime could go down by an hour per year.
Just my opinion but I think that would just increase the pain and complexity of the transition.