My guess is that the windshield had a weak spot from a rock that wasn’t visible or hidden. The heat likely exploited that defect and it cracked. Third windshield? Makes me wonder if the frame around it isn’t out of alignment. If it occurs again, ask the techs to examine it more closely for issues. Was there anything common between the previous issues? Crack in a similar location for example?
In a vehicle that size, it’s probably not necessary to vent it so the pressure doesn’t build up…but I always vent my windows by opening them every so slightly.
Of the things I miss about AZ and Ahwatukee, the heat isn’t on the list.
Good luck!