Student pilot from MLB here...
What I think the problem here at MLB is probably the controller overload...
MLB has average 366 flight a day, but because of how runways are designed, crosswind component can easily goes up to 15+kts, and GA flights has to be cancelled. Therefore most people fly as much as they can during fine days.
As far as I know, the controller who is on duty during the accident has the longest duty time. I can hear his voice almost every time I fly, and he usually do ground frequency at the same time. Because of that, he sometimes forgot or mistaken aircrafts' position.