Requeening does not always inhibit swarming.
Bees busy building comb won't swarm. Bees to crowded for brood and/or storage space will. As long as the bees are kept in a building mode swarming can be avoided. Re-queening does not solve every beekeeping problem, sometimes just the opposite.
If you're requeening constantly you are prolonging the inability of the bees to develop important behaviors like Mite Resistance, Hygenic behavior, etc. Buying queens from the Southern US and putting them in hives in the Northern US is counter productive. That practice is putting bees that are not acclimatized to the local area resulting in high die of rates during winter.
Better to buy as locally as possible, getting bees from stock that is being selected for resistence.
When I buy queens to fill out splits I plan on buying mine from Wilderness Apiaries in Port Angeles, Wa. Their bees are acclimated to the northern US and are selected for SMR and hygenic traits from survivor stock. They have Italian and Russian queens.