Look at it this way, the ride has been running for three years without incident with the lap bars. Why do we need seat belts when the lap bars would have been sufficient if the lady had put the bar on her thighs instead of her stomach? (I'm only assuming that this is what caused her to fall out)
I'm not going to speculate further as I'm not an investigator nor do I know what happened on Friday. Prayers for the family and friends of the victim.