It may mean some are pressured Snowdrops, but there are lots of overnight workers already and you are right, those hours do suit a lot of folk.
We have people putting together the internet shopping orders overnight year round, as do a lot of other companies, plus some do a lot of stock filling overnight as well. We tend to end at some point during the evening and get out of the way of the pickers. There are also transport workers, takeaway places and people involved in the distribution and delivery businesses. You generally get an enhanced hourly rate. It adds up quite nicely if you do a lot of hours overnight and means you need to work less hours overall.