There are studies showing a direct relationship to fall swarming and fall flow. Areas with goldenrod and aster, as well in the south like Florida with Brazilian peppers, have increased swarming in the fall. As much as 20% of all swarms are seen in the fall.
Over the years, many have tried to explain swarming in the fall. It may be impacted by any number of things, but the same studies had shown a lack of swarming in areas where there is no fall flow.
I've heard southern genetics, suicide bees, to about a dozen other things.
Real simple, and just like many animals and insects,,,,when food is abundance, it kicks in the natural impulse to perpetuate the species. Birds if forage is abundant, will raise additional broods, same with many other insects and animals. And in years with a deficit of food, they cut the number of litters or even the number of young raised. Why we assume that bees are not the same is beyond me. Roger Morse, Richard Bonney, and others studied this all in the 70's.