Possibly keeping their own and turfing out visitors?
Drones are particularly itinerant so probably the majority in the hive arrived at some point as visitors.
There is a school of thought that bees require a certain number of drones in the hive at any time as a factor of hive well-being/contentment.
Difficult to find concrete evidence for this. Then again, not sure any post-grad submitting a PhD thesis of 'Do drones make worker bees happy?' would get the funding?
But it certainly seems anecdotally true. Bees are very efficient: if drones were merely free-loaders, whose sperm would be unviable anyway by the next warm weather, why would they be tolerated (and continued to be fed)?