They were not over takeoff velocity at that point. They were at 120 knots when they initiated GA and slowed to 117 knots before aborting (again, the engines take time to spool up despite full thrust configuration and no braking over those seconds). Takeoff is at least 130 knots, I don't know for their exact configuration. (At max takeoff weight it's something like 153 knots, but at the end of their flight they aren't carrying a full fuel load.)