This is only speculation based on what I know about similar insects, and what little I know about SHB.
After SHB lay eggs in a hive they hatch out into a maggot looking larva which feeds in the hive until it is ready to metamorphose (?) through a pupa phase into an adult. Just like bees do inside of capped brood. Except hive beetles pupate in the ground, so they crawl out of the hive - probably attracted to light - drop to the ground where they turn into an adult beetle, mate, and fly back up into your hive to start all over again.
During cold weather I'm going to guess that those tender larva can't survive the weather long enough to crawl out and get into the ground. So I speculate that the adults either don't lay eggs during cold weather - or they lay eggs but the eggs don't hatch until it warms up.
The resident adult SHB have decreasing shelter as the cluster gets smaller, and the weather gets colder - they also have empty comb to hide in as stores get used up.
Again, largely guess work.
If you have a SBB/Oil trap and a single well guarded entrance that forces the SHBs to cross the trap while running a gauntlet of guard bees you will not only trap a lot of adults before they can get into your hive, but you will also kill a lot of the larva before they can leave the hive - before they become adults.
Maybe a hygienic trait for hive beetles will eventually emerge.