This behavour is enforced by missing nesting sites. Some more queens got killed by anxious people when they entered houses and apartements by mistake. The queen builds the combs out of a paper-like material, made out of rotten wood. For her larvae she has to hunt. The hatched workers take over for her and the colony grows quickly.
Every comb is used only one time for breeding so the hive grows by adding new combs.
Several outer hulls keep the nest climate constant. In July and August, when the number of workers reached its maximum with approx. The queens mate and search for hidden places for winter. Meanwhile, the colony dies out, the old queen doesn't lay eggs anymore and dies. The empty nest rottens quickly in autumn and winter.