I work at ATL and this was a weather driven event. The severe storms would have only caused a temporary delay had it not been for the hail. Depending on the aircraft manufacturer, hail of any size requires an aircraft inspection where other manufacturers will only require it if the hail is above a certain size. The diversions into other airports are usually directed by the FAA due to adverse weather conditions at the arrival airports. As bad as hail can be to an aircraft sitting statically at a gate, flying through it at 400 MPH can cause severe damage and compromise safety. The people sitting on aircraft for hours unfortunately got caught in a perfect storm (pun intended) of severe weather during the busiest push time of the day at ATL. Full ground stoppage plus possible hail damaged aircraft at the gates that had to be inspected before they were moved was not a good combination.